One thing that I might also think would work would be stained glass paint you can get at the craft store. its made for glass and plastic and you can get some that you can use in the dishwasher.. the only thing with that is that its permanent and will never come off.

I have had the tape and sharpie on my trackball since last Friday and the rest since Tuesday and its working out perfect.. No melting or anything. The only thing I am worried about is that over time the tape may loose its stickiness’ with moisture and other things getting to it. But I really think that would be a long term effect. So I am going to preach on the tape idea, Non permanent and easy and cheap to do.