The violet filter on the Imaging Science System aboard Voyager 1 and 2Many years ago, I said to a colleague, “What a beautiful shirt! Royal blue is a good color on you.” She replied, “What do you mean blue? This shirt is purple!” After some experimenting, we discovered that we consistently differed on the line between blue and purple. In extending our experiments to co-workers, we found that I was the outlier—most people saw blue and purple more like my colleague. It turns out that such differences are real; the proteins that detect light in our eyes can be tuned to slightly different wavelengths, and we can each have slightly different ratios of the three proteins that allow us to distinguish colors. I really do see blue where most people see purple. (Do you? Here’s a Buzzfeed quiz.)

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