Clear buttons with the UV might look awesome (assuming you can see them).

Interesting! 'Course, if you had very clear buttons and spent a lot of time in the car, you might wind up with this odd, cross-shaped blotchy tanned spot on your forehead!

Rather than clear, you could use these to fluoresce some of the colored fluorescent dust that has been mentioned here. How about: buttons with a just a touch of white and black pigment (to make a translucent milky grey, with some of the fluoro-dust mixed in (apparently that stuff is white in daylight).

I might have to get a few of these just for fun. A practical consideration: I wonder if they are available in surface-mount configuration for knob illumination?