I was diagnosed with color blindness as a child. I was told I was red-green color blind. However, this never made much sense to me, because I can tell the difference between red and green
OK, yes, I can. But reds seem duller to me. I have what is sometimes called "red weakness." There are three basic photopigments (colors) we humans see: red, green, and blue. People with normal sight are trichromats, whereas people we normally think of as color blind are monochromats: they see no pigment at all, or only one color (usually blue, the shortest wavelength).
Then there's dichromats, who cannot see one of the three wavelengths. I'm a trichromat like most people, but an anomalous one. Specifically, I am protoanomalous trichromat, which means my red photoreceptors are abnormal.
This explains some of why my wife says I can't tell the difference between various colors, but she thought it was all in my mind, because I can tell the difference between red and green, despite my story about what the doctor told me when I was a kid. I showed her two pictures, showing what a normal person sees, and what someone like me sees. My problem isn't very acute, and I can see the number "2" in the normal picture, but I have to strain for it. I can see some difference between the two pictures, but it is very slight. My wife sees a significant difference between the two.