How every fact on this site was checked
88 facts. Each one is in our own words, each one has a source, and each one was checked against that source on 13 November 2026.
How we check
We read each source and wrote each fact in our own words. Our build stores the text of every source page, and for each fact it checks that the key words and figures, the “checks” in the table, really appear on the source page. If any check fails, the site does not build. Where good sources disagree, we show each version in a “Sources differ” box rather than picking one. Anything that is our own reading, rather than a sourced fact, is labelled Our opinion.
Our own drawings
Every picture on this site is our own drawing. We don’t reproduce the famous originals (the dress photo, Kitaoka’s tart, Adelson’s figure); we make our own versions of the same idea and say so. Where we state a colour value in a caption, such as the grey in our checker scene, it describes our drawing, not a sourced fact.
Known disagreements
- The real colours of the dress. Black and blue under good white light (Michael Bach); blue (WIRED); blue and orange, from the photo’s pixels (Bevil Conway, quoted by WIRED).
- Who found Benham’s colours first. Gustav Fechner in 1838 (Bach); Benedict Prévost in 1826 (Richard Gregory, quoted by Bach); Charles Benham made the top famous in 1894.
- Neon colour spreading. First described by Van Tuijl in 1975 (Bach), though Bach’s reading list includes Varin’s 1971 paper on colour spreading.
- Red’s opposite colour. Green in many textbooks; blue-green, says Bach.
What we left out
- Survey figures for how many people saw each version of the dress did not appear in the sources we could check, so we leave them out.
- Explanations of why some illusions work are still debated; where a source says nobody knows for certain, we say so.
The log
| # | Fact | Source | Checks |
|---|---|---|---|
| 1 | In February 2015 one photo split the internet: was the dress blue with black lace, or white with gold lace? | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 2 passed |
| 2 | Michael Bach calls it a social illusion: it only gets interesting when you compare notes with other people. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 2 passed |
| 3 | It has nothing to do with colour blindness. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 1 passed |
| 4 | The colour of a non-glowing thing like a dress depends on two things: the colour of the light falling on it, and how its material reflects each colour of light. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 2 passed |
| 5 | Your visual system tries to work out the colour of the light and ‘subtract’ it. This is called colour constancy, and it usually works well. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 3 passed |
| 6 | That is why a photo taken on a glacier at noon can look surprisingly blue when you look at it at home. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 1 passed |
| 7 | Bach blames a poor photo: badly lit, overexposed on one side and showing only the dress, so the brain has too little to go on when it guesses the light. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 3 passed |
| 8 | Colour names play a part too: a bright, bluish colour counts as ‘white’ for some people and ‘blue’ for others. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 2 passed |
| 9 | Look at two stripes through small holes, cut off from the rest of the picture, and the argument mostly goes away: both sides tend to see brownish and light bluish. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 2 passed |
| 10 | It has been called the ‘Necker cube of colour vision’: two readings are about equally likely, but unlike the Necker cube it is hard to flip between them yourself. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 3 passed |
| 11 | Bach’s answer to the real colours, well lit with white light: black and blue. | Michael Bach, Optical Illusions & Visual Phenomena: The dress | 1 passed |
| 12 | WIRED’s verdict in 2015: the dress is blue. | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 1 passed |
| 13 | Neuroscientist Bevil Conway ran the pixels through Photoshop and decided the dress was actually blue and orange. | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 1 passed |
| 14 | Conway, of Wellesley College, suggested that people discount either the blue end or the gold end of daylight’s colours, and so see white and gold or blue and black. | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 2 passed |
| 15 | Daylight itself changes colour, from pinkish red at dawn to blue-white at noon and back to reddish at twilight. | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 1 passed |
| 16 | Jay Neitz, who saw white and gold, said that in 30 years of studying colour vision it was one of the biggest individual differences he had ever seen. | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 2 passed |
| 17 | Pixels that some people saw as gold measured R 93, G 76, B 50: on their own, a kind of orange. | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 2 passed |
| 18 | Conway joked that night owls might be more likely to see blue and black. | WIRED: The science of why no one agrees on the color of this dress (Adam Rogers, 26 February 2015) | 2 passed |
| 19 | Akiyoshi Kitaoka’s famous picture shows a strawberry tartlet with a blue-green tint, and yet the strawberries still look red. | Michael Bach, Optical Illusions & Visual Phenomena: Strawberries are not red | 2 passed |
| 20 | There is not a single red, or even reddish, pixel in it. | Michael Bach, Optical Illusions & Visual Phenomena: Strawberries are not red | 2 passed |
| 21 | Mask off just the ‘reddest’ parts and the red mostly disappears. | Michael Bach, Optical Illusions & Visual Phenomena: Strawberries are not red | 1 passed |
| 22 | Swap the strawberries for ovals of the same colours and the ovals still look reddish, so it isn’t only that we know strawberries are red. | Michael Bach, Optical Illusions & Visual Phenomena: Strawberries are not red | 2 passed |
| 23 | Expectation does play some part: there is evidence that it affects colour perception to some degree. | Michael Bach, Optical Illusions & Visual Phenomena: Strawberries are not red | 1 passed |
| 24 | Kitaoka made it in 2015, and Bach calls it a strong demonstration of colour constancy. | Michael Bach, Optical Illusions & Visual Phenomena: Strawberries are not red | 1 passed |
| 25 | The mostly green-blue picture shifts what your eye takes as white, so grey and white areas look reddish. | Michael Bach, Optical Illusions & Visual Phenomena: Strawberries are not red | 1 passed |
| 26 | In 1824 the chemist Michel-Eugène Chevreul became director of dyeing at the Gobelins tapestry works, and soon got complaints that the colours looked dull. | Encyclopaedia Britannica: Michel-Eugène Chevreul | 2 passed |
| 27 | He found the problem was not chemical but optical. | Encyclopaedia Britannica: Michel-Eugène Chevreul | 1 passed |
| 28 | His law of simultaneous contrast: colours placed side by side affect each other, each pushing its own complementary colour onto its neighbour. | Encyclopaedia Britannica: Michel-Eugène Chevreul | 1 passed |
| 29 | He set it out in 1839 in his most influential book, The Laws of Contrast of Colour. | Encyclopaedia Britannica: Michel-Eugène Chevreul | 1 passed |
| 30 | He described ways to get colour effects, such as massed dots of single colours. | Encyclopaedia Britannica: Michel-Eugène Chevreul | 1 passed |
| 31 | He arranged all the colours of the spectrum in a circle to show how they relate. | Encyclopaedia Britannica: Michel-Eugène Chevreul | 1 passed |
| 32 | Before all that, he patented a new kind of candle, made with stearic acid from fat, in 1825. | Encyclopaedia Britannica: Michel-Eugène Chevreul | 1 passed |
| 33 | In Bach’s eye demo, a grey eye with a red tint around it looks bluish, while the identical grey eye on the other side looks neutral. | Michael Bach, Optical Illusions & Visual Phenomena: Colour in context | 1 passed |
| 34 | The reddish surround pushes the grey towards its opposite colour, which for red is blue-green. | Michael Bach, Optical Illusions & Visual Phenomena: Colour in context | 1 passed |
| 35 | Bach calls it simultaneous colour contrast, probably helped by colour adaptation. | Michael Bach, Optical Illusions & Visual Phenomena: Colour in context | 1 passed |
| 36 | In Ted Adelson’s checker shadow, a square in the shadow of a cylinder looks brighter than a square outside it. | Michael Bach, Optical Illusions & Visual Phenomena: Adelson’s checker shadow | 2 passed |
| 37 | In fact the two squares have identical luminance: the same amount of light comes from each. | Michael Bach, Optical Illusions & Visual Phenomena: Adelson’s checker shadow | 1 passed |
| 38 | Our eyes are not light meters: they take context into account. | Michael Bach, Optical Illusions & Visual Phenomena: Adelson’s checker shadow | 1 passed |
| 39 | Your brain estimates the lighting and judges the material: is this a light or a dark square, whatever the shadow? | Michael Bach, Optical Illusions & Visual Phenomena: Adelson’s checker shadow | 1 passed |
| 40 | Adelson published it in 1995. | Michael Bach, Optical Illusions & Visual Phenomena: Adelson’s checker shadow | 1 passed |
| 41 | In White’s illusion, identical bars look different in brightness depending on which stripes they sit on. | Michael Bach, Optical Illusions & Visual Phenomena: White’s illusion | 2 passed |
| 42 | Michael White described it in 1979 and 1981. | Michael Bach, Optical Illusions & Visual Phenomena: White’s illusion | 1 passed |
| 43 | Lateral inhibition, the usual explanation for contrast effects, predicts the opposite of what you see. | Michael Bach, Optical Illusions & Visual Phenomena: White’s illusion | 1 passed |
| 44 | Mach bands: where dark ramps up to light, you see a bright band at the top of the ramp and a darker band at the bottom that are not really there. | Michael Bach, Optical Illusions & Visual Phenomena: Mach bands | 1 passed |
| 45 | They have been known since 1865. | Michael Bach, Optical Illusions & Visual Phenomena: Mach bands | 1 passed |
| 46 | They appear where a gradient of brightness, or colour, bends. | Michael Bach, Optical Illusions & Visual Phenomena: Mach bands | 1 passed |
| 47 | In Bach’s assimilation demo three discs behind coloured grids look cyan, magenta and yellow, but all three are white (strictly, a light yellow). | Michael Bach, Optical Illusions & Visual Phenomena: Colour assimilation | 2 passed |
| 48 | This is assimilation, first described by Bezold: each disc takes on the mixed colour of the lines crossing it. | Michael Bach, Optical Illusions & Visual Phenomena: Colour assimilation | 2 passed |
| 49 | Assimilation is the opposite of colour contrast. | Michael Bach, Optical Illusions & Visual Phenomena: Colour assimilation | 1 passed |
| 50 | Bach admits he doesn’t understand the brain mechanism behind assimilation. | Michael Bach, Optical Illusions & Visual Phenomena: Colour assimilation | 1 passed |
| 51 | One idea, from King in 1988: we see contrast when patches look like separate things, and assimilation when they look like one whole. | Michael Bach, Optical Illusions & Visual Phenomena: Colour assimilation | 1 passed |
| 52 | In the Munker illusion two stripes look green and blue, yet there are only three colours in the picture: both stripes are the same green. | Michael Bach, Optical Illusions & Visual Phenomena: Munker illusion | 2 passed |
| 53 | It shows how much the colours around something change how we see it. | Michael Bach, Optical Illusions & Visual Phenomena: Munker illusion | 1 passed |
| 54 | Hans Munker wrote about coloured grids in 1970. | Michael Bach, Optical Illusions & Visual Phenomena: Munker illusion | 1 passed |
| 55 | In the watercolour illusion, shapes edged with a dark wavy line and a lighter coloured line inside look faintly tinted, though the inside is plain white. | Michael Bach, Optical Illusions & Visual Phenomena: Watercolour illusion | 1 passed |
| 56 | Baingio Pinna discovered it in 1987. | Michael Bach, Optical Illusions & Visual Phenomena: Watercolour illusion | 1 passed |
| 57 | Even with pale lines the illusory colour is quite strong. | Michael Bach, Optical Illusions & Visual Phenomena: Watercolour illusion | 1 passed |
| 58 | Bach suspects map colourers knew about it centuries ago. | Michael Bach, Optical Illusions & Visual Phenomena: Watercolour illusion | 1 passed |
| 59 | Neon colour spreading: a coloured star set inside black lines seems to glow, so it looks a little like a coloured disc. | Michael Bach, Optical Illusions & Visual Phenomena: Neon colour spreading | 1 passed |
| 60 | Any gap between the coloured and black lines destroys the effect. | Michael Bach, Optical Illusions & Visual Phenomena: Neon colour spreading | 1 passed |
| 61 | Bach says Van Tuijl was the first to describe it, in 1975. | Michael Bach, Optical Illusions & Visual Phenomena: Neon colour spreading | 1 passed |
| 62 | Bach’s own reading list starts earlier, with D. Varin’s 1971 Italian paper on contrast and colour spreading. | Michael Bach, Optical Illusions & Visual Phenomena: Neon colour spreading | 1 passed |
| 63 | It works with greys too. | Michael Bach, Optical Illusions & Visual Phenomena: Neon colour spreading | 1 passed |
| 64 | An afterimage is an illusion in which the picture on your retina lingers after the thing itself has gone. | Encyclopaedia Britannica: afterimage | 1 passed |
| 65 | It can be positive, matching the original, or negative: less bright, or in the complementary colours. | Encyclopaedia Britannica: afterimage | 1 passed |
| 66 | A common one is the spot you see after a camera flash. | Encyclopaedia Britannica: afterimage | 1 passed |
| 67 | In the lilac chaser, a ring of magenta blobs circles a cross, and one blob at a time briefly disappears. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 68 | Keep your eyes on the cross and you see a green spot running round the ring. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 69 | With a really steady gaze the magenta blobs fade away completely, leaving only the green spot. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 70 | Bach notes that the opposite colour of red is not green, as many textbooks say, but blue-green. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 71 | Its inventor, Jeremy Hinton, says it shows Troxler fading, complementary colours and negative after-effects. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 2 passed |
| 72 | We normally move our eyes about three times a second, so afterimages rarely build up in everyday life. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 73 | Research has traced the afterimage to retinal ganglion cells, in the eye itself. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 74 | An afterimage normally fades within a few seconds. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 75 | Your brain joins the afterimages, one place after the next, into a single moving green disc. | Michael Bach, Optical Illusions & Visual Phenomena: Lilac chaser | 1 passed |
| 76 | The McCollough effect: after a few minutes of looking at coloured stripes, black and white stripes look faintly coloured. | Michael Bach, Optical Illusions & Visual Phenomena: McCollough effect | 1 passed |
| 77 | Most aftereffects last a minute at most. This one can last hours. | Michael Bach, Optical Illusions & Visual Phenomena: McCollough effect | 2 passed |
| 78 | Ten minutes of adapting is said to give an effect lasting months. | Michael Bach, Optical Illusions & Visual Phenomena: McCollough effect | 1 passed |
| 79 | Bach warns that trying it changes your brain for a long time, up to months. | Michael Bach, Optical Illusions & Visual Phenomena: McCollough effect | 1 passed |
| 80 | Benham’s top is a black and white disc that, when it spins, shows faint colours. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 1 passed |
| 81 | Take a photo of it spinning and the colours are not there. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 1 passed |
| 82 | Spin it the other way and the colours swap places. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 1 passed |
| 83 | In 1894 the toy maker Charles E. Benham sold his disc as an ‘Artificial Spectrum Top’. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 2 passed |
| 84 | Bach says Gustav Fechner was the first to describe the effect, in 1838. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 1 passed |
| 85 | The psychologist Richard Gregory traced it back further, to a French monk, Benedict Prévost, in 1826. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 1 passed |
| 86 | Prévost saw colours ‘like a heavenly light’ on his fingers when he waved his hands about in the cloisters. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 2 passed |
| 87 | The effect was forgotten and rediscovered no fewer than twelve times. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 1 passed |
| 88 | Nobody knows for certain why the colours appear. | Michael Bach, Optical Illusions & Visual Phenomena: Benham’s top | 1 passed |