When I was 12, I became part of the very select group of people who have had a life-changing experience at a fondue restaurant. After repeatedly grabbing my brother’s green fondue fork and eating his steak from the broth pot, I found myself accused of elder-sibling entitlement. But my father, who is colorblind, said I had done nothing wrong; like me, he was unable to see any difference between my brother’s green fork and my orange one. The Ishihara color-vision test he administered on his computer later that night confirmed that I was among those few women with red-green colorblindness. He was excited that I saw “correctly” — which is to say, like him. Back then, the ability to understand his frame of reference was mostly limited to other people barred from becoming astronauts. Now there’s an app for it.

Colorblindness can be sort of a fun affliction. Sometimes I see my own private colors, and objects lose their prescribed meanings. Someone’s fashionable, Instagram-friendly sand-colored apartment might become, just for me, a garish baby-food green. The English scientist John Dalton described something similar in “Extraordinary Facts Relating to the Vision of Colours” (1794), the first known scientific study of anomalous color vision: He would often earnestly ask people whether a flower was blue or pink “but was generally considered to be in jest.”

I attended a liberal-arts college, so I know full well that philosophizing about the subjective experience of color is best done barefoot in a field while listening to Alice Coltrane music. Biologically, though, the mechanics are relatively straightforward. Humans are trichromats: We see color because three sets of cones inside the eye absorb light at different wavelengths, from red to blue. Colorblindness is, typically, a congenital weakness in one set or another. The cones in my eyes that are meant to detect long red wavelengths are abnormal; I may see red and orange, but they’re dim and green-tinted, their energy registering partly on the cones that detect medium-length green wavelengths. (For some colorblind people, the entire season of “autumn” must feel like an elaborate prank.) Those with no working cones in one group — dichromats — experience almost total blindness of that color. Red becomes black. Orange, now redless, becomes yellow.

Eight percent of men have abnormal color vision, but only half of 1 percent of women. My life with it has been fairly normal, save for the time I wore all purple on the Fourth of July. There are times, though — looking over a map, a painting, a color-coded spreadsheet — when seeing color in high fidelity is important. And this is how, while researching expensive color-correcting glasses, I came across Color Blind Pal, a free smartphone app that helps colorblind people navigate the world.