Every year, the Alan Alda Center for Communicating Science runs The Flame Challenge, a competition that asks scientists to answer questions like “What is a flame?” in a way that makes sense to an 11-year-old. In fact, children judge the entries. This year’s challenge was to answer the question “What is color?” My training is in vision science, so I thought I would give it a try.

What follows is my entry.

Stare at your eyes in a mirror and you’ll find that the dark circle in the middle is a hole! If it weren’t so dark in there, you would be able to see part of your brain: the “retina”, a thin sheet that detects the light inside your eye. We use that light to see everything around us.

Light comes in many shades, called “frequencies”. They can be spread out to create a rainbow: red, orange, yellow, green, blue, indigo, violet. One of the first science experiments on light was by Isaac Newton, who used a piece of glass to put the rainbow back together again, creating a bright white light.

When light hits an object, only some of it bounces back to our eyes. Color is how we perceive the mixture of frequencies of light that bounces back. Colors look different depending on what is around them, which causes many amazing visual illusions that you can find online.

Humans aren’t the only ones who see in color. Animals and insects do too. It’s amazing — some animals (like the mantis shrimp) have such fancy eyes that they see colors that no human can even imagine! The mantis shrimp must think that we are all colorblind.

Does everyone see colors the same way? Is my red your blue? Nobody in the whole world knows the answer to that question. Maybe you can figure it out!