I've known for 30 years that I was colour confused, it was diagnosed during my pre-hire medical at IBM. I've always described it symptomatically, as in "certain pinks and purples appear grey, my favourite brown shirt is green, but occasionally, I'll see a hint of green". And I've long thought that my CC was partly influenced by diet (the shirt would be greener after meals in certain restaurants, but I could never pin down the magic ingredient combo).
I have it on good authority that Mars is red, but I see it as a faint light of undetermined colour.
I had my eyes checked last week. I said all of the above to the examiner. He said something along the lines of "Huh, I've never heard of that before".
Then I described how I have a hard time scooping the yard: I have to work really hard to see the shit for the grass, but when I do, it becomes more obvious. There isn't enough contrast for me to pick it out without cognitive effort, but with said effort it becomes clear.
"Huh", he said, "It sounds like you have a very mild form of red-green colour blindness".
Interesting. I've never had a problem with traffic lights, red is one of my favourite colours, and I love the infinite variety of greens of spring. But picking a cardinal out in a dark green tree is tough - do-able, but tough. It's much easier in a light green tree.
So two weeks ago I would have answered "different form" but today I chose "mild R-G".
As my daughter would say, "That was a great old man story, thanks for sharing".