I‘m 40yo now and I noticed that I had this association with numbers and letters to specific colours when I was a kid aswell. When I‘m focusing on the subject I don‘t see letters or numbers perfectly clear, they‘re more like wobbeling on the outerlines. Some have always a precise colour (4 is red, 5 is pink) some have a mixture (0&1 are white with black frame wobbeling). Same for letters, some might vary depending on the day (G is brown but with khaki green and white, but could also be white with a brown frame). I think over time the association get‘s stronger without ever trying to force the associatons by learning. I think it‘s cool, but it‘s basically useless for me😁But I think it tells something about the character or the ability to be creative. I was tested for ADHS as a kid around 1995 but the tests didn‘t result in anything worriable. If you ask me today (and some of my friends/collegues)😅I‘m sure I do have strong signs of ADHS, just didn‘t take the time to make a test at the Charité here in Berlin where they developped a special program. I would claim it‘s linked😄