Sneak preview of the "ColoredNoteWithText" Icons with a separate 16x16 design.
(There's a version without separate design for the 16x16 size too, but these 16x16's are not as nice).

I'm quite sure that there's no "official" color for each music file type.
Variations on a color is a good idea, but the problem is that it's very difficult to see the difference between the variations. I'd like to see what file type it is in one blink of the eye. That's why the colors have to be different enough from each other.
File icons like m4b and m4p (maybe, but better buy unprotected instead...) will be added in the future.
I don't plan to add icons for wav, mid, midi, rmi, rm, Tracker formats, Module formats, ... as they are no real "music" formats (in my eyes). I do play them though. At max, a "global" icon can be used for these.
These are the "MonkeyOnly" Icons:

with either this

or this

as 16x16 icons.
For people not familiar with icon files: all sizes (48x48, 16x16, ...) are stored in one single file, with each size in different number of colors.
The included sizes are 48x48, 32x32 and 16x16. The included number of colors are 256 and XP (True Color).
These are just 2 types of icons. I plan to add more in the future (as already shown through this thread).