Do you mean
ALT+O >
Display? On that options screen there are 3 drop down boxes with colours in them. They represent the colours of the letters on the switchbar buttons.
I've never looked into how people change the switchbar buttons themselves because I have never wanted to, however, it's probably through the use of some DLL, I should imagine someone else could go into more detail (and clue me up at the same time
)
Regards,