It's black and blue. Here's the science behind why it looks different for different people.

It's black and blue.

The science of why people saw the dress differently is a little complicated, and scientists offer different explanations for some of the details. The peer-reviewed Journal of Vision even published several articles about it.

Stated plainly, the way your brain determines color relies on two things: the color of the object you're seeing and the color of the light source. The image was overexposed, meaning the light in the image overwhelmed the color of the subject. Parts of the dress were also in shadow. This all implies that the dress had a partial light makeup of bluish shadow, reflecting off the dress itself, and yellow light, from the store's bad lighting. Parts of the image also seem to indicate that the dress is backlit.

Depending on whether your brain saw the dress more in shadow or more in a direct light, you'd see the colors differently.