While UV light may have a bad effect on brake fluid, it's not a concern you need to be worried about if you change your brake fluid as often as you should.
I go every other year on the street bike and twice/year on the race bikes.
The res. is very opaque to begin with, there's not much light getting through there in the first place. If there is fluid leaking out of res., you have a serious problem, fix it, and not with just a wrist-band to soak it up. I'd assume that either means you have a leak (VERY BAD), or have over-filled it (VERY BAD).
It does add a personal touch to your bike, and for that, it's very cool
