Dogs or cats? Juices or smoothies? Blue and black or white and gold? These are the great questions of our time. And now, at least for that damn dress, we have an answer. First, it's worth noting that both the Tumblr user who originally posted the dress and the retailer of The Dress both agree that, IRL, it's blue and black. So, why do so many people see it so completely differently? "Often, when you get these large perceptual effects, it’s the confluence of many small things contributing to it," says David Brainard, PhD, a psychologist who studies visual perception at the University of Pennsylvania. These small factors include: the device on which you're looking at the picture (phone or laptop?), the angle from which you're viewing, the lighting in the room you're in (or maybe you've even ventured into actual sunlight?), and the site you're looking at (the blue background of Twitter versus R29's white one). All of these can play a part in what colors you think you see. However, perhaps most interesting is what this shows about how our brains interpret color: "It turns out that our brains are constantly adjusting, in some sense — like an automatic white-balancer," says Dr. Brainard. "They are automatically adjusting under the conditions in order to stabilize the [way colors] look." This means that where you look first in the image can have a huge impact on what you see next. For instance, if you start in the upper-right corner (in which the light looks a little bit bluer) you might see the dress differently from someone who started in the lower-left corner, where the light has a yellow-y hue. To compensate for what it perceives as yellow-colored light, your brain will sort of "turn down the yellow knob," Dr. Brainard explains, making the dress look more blue. But, even with all those factors, there's no denying that The Dress has captured something particularly unique. What is it that makes the same person see the same dress very differently at different times? "We have principles that might explain it," Dr. Brainard says, but people's differences in perception (and the vehemence with which they defend them) make this dress an unusually striking example. So, where do you stand?