Some People May See Colors the Rest of Us Can’t Even Imagine

Most of us move through the world assuming color is shared. A red apple, a blue sky, a green field — they feel like common experiences, as if everyone is seeing roughly the same thing with different preferences attached.

But color vision is not that simple. Some rare people may have a fourth type of cone cell in the retina, a condition called tetrachromacy, which could allow them to distinguish colors that look identical to the rest of us. The hardest part is not imagining it. The hardest part is proving what their private visual world actually looks like.