https://en.wikipedia.org/wiki/Congenital_red%E2%80%93green_color_blindness

It's quite common in it's mild forms. I never noticed it till after shop-class when I was really good with the theoretical aspects of electric circuits, but on the practical pieces I always put in the wrong resistors ... because they were colour coded with shades of green/red/brown that kind of look the same for me. I even argued with my teacher that I did in fact put in the correct resistors, but he won because it actually wasn't working ...

Only a few years later when doing a vision exam during mandatory conscription that they just blatantly asked me if I was colourblind ... and at first I was like .. "no?". But they said that results said I was ... and suddenly shop class made sense ...