One thing to try might be "vinyl dye" It's used for automotive touchups mostly but a lot of people in the PC modding community use it for coloring diskdrives and such.
It applys like a spray paint but it actually dyes the plastic instead of just covering it, and it's supposed to be a lot better especially on power buttons and cd eject buttons that see more wear.
I thought about doing this same thing- all black buttons with lettering on them, but found some lightup atari-style starts instead