They have to colour wheels to make them white. The urethane they make wheels out of is naturally beige colour.
It's turning pretty scary here with everyone swearing allegiance to the white wheel. Y'all gonna mount a lynch mob and head down to the nearest skate store to roun' up all dem coloured wheels?
I think I've only seen one set of "natural" colored wheels in my life.
This white wheels hysteria started in the '80s when manufacturers suggested that the pigments used to make colored wheels made them slower (such things were once discussed in TWS's short-lived technical column with professor Paul Schmitt). My first set of Black Vision Blurrs literally felt slower and softer to my friend's identical natural ones. I guess white is kind of similar to undyed urethane, so people have continued the delusion that white wheels are the fastest. By now there should be no difference in performance.
The black grip theory went the same way. At one time, black was the best performing griptape. Maybe Mr. Paradox can shed some light on this subject, but I'm pretty sure that if sandpaper, save for the really fine grit gray-ish stuff, normally comes in an earth red color, then maybe they have to add unnecessary pigments to make it black.