The recent viral photo of a dress of controversial colour demonstrates that the perception of colour is a complex psychovisual phenomenon that involves not just the physical electrical impulses produced by the light receptors in the retina but also interpretation by the brain based on context and expectation. It also underscores the importance of getting your exposure and whitebalance correct.
Philosophers have used colour in debates about the notion of “qualia“, or the “the ways things seem to us“. From a photographic perspective, we can understand how a dress which under normal lighting looks to be royal blue with black lace can look in the photo to many people as being white with gold lace. There are two issues with the disputed photo that contribute to the confusion, it is badly exposed and the auto white balance is extreme.
I assume that the photo was taken by a phone and that the autoexposure was fooled by the darkness of the dress. The photo was consequently overexposed leading the royal blue parts of the dress being rendered a much lighter shade of blue. The dark lace parts of the dress are also brightened and now longer looks black.
The second issue is that the camera then tries to colour correct the image by setting a white balance. It misinterprets the scene as being taken under high colour temperatures, e.g. at dusk with the illumination of a clear blue sky. To compensate, it changes the colours in the scene, effectively trying to make the blue dress look more white as it assumes that this is “actual” colour of the dress. To bring blue closer to white, the camera adds yellow to the scene (you can tell from the yellow colour cast to the background). The dark lace of the dress, already made a lighter shade by the overexposure, is now given this yellow colour cast which can be interpreted as being a golden colour, especially in the context of the rest of the dress which is rendered as palish blue.
These two effects combine with the way the brain tries to work out what the colour of objects are from visual stimuli. Since our vision has to operate under many different types of lighting, what we perceive as colour of an object is not actually the actual colour cone responses, but what our brain retrodicts based on our assumptions about the lighting. An apple under noon day lighting will look different compared with viewing at dusk, but we don’t usually say that the apple has changed colour because our brain will take the different lighting conditions into account and interpret that the apple is the same colour. The case of the dress is simply a case of the camera being fooled together with the way our vision system operates.