synaesthesia
I probably wouldn't have said that if I hadn't just been reading about it. Hmmm. I often get orange and green mixed up and transpose a lot of letters and some numbers. For example, I often type "a" instead of "i" when refering to myself and sometimes type "2" instead of "s" and "7" instead of "f". I also sometimes get "s" and "z" wrong. Maybe that's not synaesthesia at all, but it's strange.
Edit: Hmmm. Looking at those letters/numbers it appears they are nearly mirror images of each other and orange/green are nearly opposite colors or at least I preceive them that way. Strange.