It's definitely true that lighter colored stones seldom show up in our collection. There are a few good reasons for this.
A lot of pale/white rock is quartz/granite based, and is made up of actual crystals ranging in size from a grain of sugar to... well, several inches across.
Since we have deliberately made the choice to only work with naturally tumbled beach stones, we have to work with what we can find. Most of the time, these pale stones never get truly smooth surfaces-- their surfaces are more like the skin of an orange, and the numerous tiny "pits" cause paint to flow in all sorts of directions... mostly directions where I don't want paint.
The mandala patterns on Alchemy Stones are extremely accurate and detailed... so it's simply not possible to paint them on a "rough" surface. That said, some of our large "Garden Stones" often have less smooth surfaces... it works because the level of detail on Garden Stones is much lower.
One final issue I come across is that many pale stones (especially in the granite family) are not a uniform color-- they are actually patterned and multi-colored, like a granite kitchen countertop. Why is that a problem? That's a matter of personal aesthetic preferences, I suppose-- I just can't get it to "look right," a bit like trying to wear plaid and stripes together-- it hurts my eyes!
All that said, I do occasionally come across pale stones that turn out to be smooth enough to paint... and they offer a lovely contrast background for darker paint colors, as show in a couple of examples here.
Occasionally I hear "Why don't you just put the pale rocks in a rock tumbler?"
Well, whereas that might work-- in the functional sense-- it goes against our intention that Alchemy Stones are "natural" and come to you unaltered, with nothing but surface decoration added.