wow this is really weird...
I've always thought of months, days of the week, grades at school, subjects at school, numbers, hours of the day, notes on my viola, and probably a lot of others, as each having a specific colour. I had noticed it before, and I find it very helpful for organising stuff, but I had no idea that it was actually a scientifically recongnised phenomenon and has a name:
Grapheme-colour synesthesia - Wikipedia
Man, I love wikipedia.