Our brains make these unconscious choices all the time. Think of a white piece of paper under a streetlight; it might look orange. But in this case, we know the paper is white to begin with, and that it’s being lit by orange light. We know a lot more in that situation than we did with the picture of the dress. That is, if we know the paper is white to begin with, we know the light is orange to begin with, and we’re not confused if the paper looks a little orange. Unfortunately, cameras aren’t always as good at compensating for different-colored light as we are. In the picture of the dress, the background is blurry, and the color of the light in the picture of the dress is ambiguous.
When we look at the photo, we know instantly that it looks different from the way the dress would look in real life. The background is very bright, and as a result, we have few hints about what the photo’s light looks like in real life. The light could be orange like a living room or a streetlight, or it could be blue like sunlight or a daylight bulb. Some of us subconsciously decided the light was orange; others decided the light was blue. Which color we chose affected our perception of the color of the dress, on which that light was shining. That subconscious choice nearly tore us all apart Thursday night—it might have broken up Kimye.