AFAIK, it's not in the rules. Therefore, it's different from country to country. Most important for amateurs in tournaments is to play from the colour given by the Commitee.
In Germany, we know men's tees in descending order as white (tips), yellow (regular), blue (uncommon, seniors). Red (regular) and orange (Seniors) are ladies' tees descending. We had black for "ladies tips" but this was discarded a few years ago.
St.Andrews has white, yellow, red with the same meanings.
I've seen different colours at USA courses and I think these are copied here (e.g. blue replacing white). The only real common term seems to be "red = ladies", with exceptions.
In WGTland, you might take black for Legend tees (sometimes).
Edit: Some WGT tee orders:
BPB, CCC, OLY: Black, blue, white, red
OAK: Green, blue, white, red
KIA: Black, yellow, white, blue
MER: Black, gold, white, red
PIN: Yellow, blue, white, green
Quite differing as you may see.