I seem to remember that people were using Rit dye to color their Model M keys.
I have purple keys on mine. Prefer it to the red, personally. And yes, Rit dye all the way.
I got mine from a Dentist here named SKCheng. He got it from Unicomp.Show Image(http://farm5.static.flickr.com/4126/5013170200_8b251fcd5c_z.jpg)