Bases come in two varieties, mainly - die cut's with solid color (think K2 Hellbent) and clear base material that has graphics screened on the back (our skis for example).
If its clear translucent material, use clear P-tex, and it'll probably look shitty. If its white opaque material, use white (if you can find it) or black P-tex, and it'll look shitty.
Unless you have a lot of practice, you'll eventually get one of your fixes to last more than a single day of skiing, and by that time, you'll have done more damage trying to patch it than the initial shot to the base and wont care what color that fucker is.