Damn, great idea.
You can order faceplates and buttons from
DecalGirl or
Xtreme Enterprise.
They do have yellow, red, and blue buttons, but the way the buttons are set up, they're all attached as one.
I guess you could cut the buttons apart, but it'd be a task in itself.
Unfortunately, I know that
someone makes gray buttons, but I haven't been able to find any.
And, I haven't even heard of green buttons...
Good luck though.