This is a plug-in for the addon Masque and without having it installed you will just waste 252 KB of space on your hard drive.
UPDATED for 6.2.0 Fury of Hellfire!!
I decided to do another version of my "Masque_ClassButtons" skin. I wanted to make it cleaner (sorta did that) and also join the pixel brigade. Didn't quite do that one. I made it two pixels wide, that are class colored, with a one pixel black surround on both the inside and outside. It looks OK, but I may have ended up making it too big. It's got a blue highlight and red "pushed" texture, and a green "equipped" texture. It has a pink-ish "checked" texture, too, just like the "ClassButtons" skin has. It has a "gloss" texture, also, and you can use Masque to fine tune that one.
This "skin" works best (in my opinion) if you scale back your action bars to about 80%. That's what I did in the picture. I've found that some icons in the game aren't showing correctly with this skin. I don't know why, either.
I hope you like it, but won't be broken up over it if you don't.