"I NEED A BRAKE RESERVOIR BAND SO THE SUN DOESN'T RUIN MY BRAKE FLUID."
Sunlight won't hurt your brake fluid-it's water that will destroy it, and an elastic strip of terrycloth won't do much in prevention of the latter anyways. The wristband that racebikes have been sporting for years is merely a preventative measure for any leaking brake fluid-the stuff is slippery, you know. In the hectic pace of a race team's pit area the wristband can sometimes soak up a bit of hastily poured fluid, and in a crash help to keep the cap on.
The trend has made its way into the street scene, but it's more for fashion points than function.