My husband and I went to an exhibition about the solar system at our local natural history museum. There was also an exhibition for children about the human body with really good explanations how genes work, how our ear works, stuff like that.
We came to the part about the eyes and there was an explanation of colorblindness and the different forms together with the tests. You know - the circles with dots where you have to read the number. Anyway, I forgot why but he started reading out the numbers. And well, he got one of them wrong. Not the test for full-on red-green blindness, but he can’t tell certain shades apart.
In hindsight I had noticed that he sometimes confuses names for colors apart from the basic ones or that he doesn’t like it when I identify an object by its color (e.g. “give me the pink one”). But I’d always chalked it up to German not being his mother language.
To add experience to your description: I can easily tell the difference between a red light and a green light. I however did not know that the walking person symbol (USA) is in fact white, not green.
I always just assumed it was green until I had an embarrassing conversation with someone from Indonesia I was hosting who said,
“Crossing in this country is so easy; I just wait for the white man and then I go.”
I thought he was just being low-key racist and started to point out that the area we were in didn’t have very many white people around until he clarified he was just talking about the crossing signal.