You would generally buy your new cabs professionally painted by Yorketowne or a similar company. They will almost certainly have a shade of gray, if not a couple. Often you can specify a BM or SW shade for custom colors but it might cost a bit more. Is it a waste? Not if it's what you want. Generally a "paint grade" of lumber will be used, meaning the grain is not perfect enough for stain. I suppose some folks do buy unfinished cabs and paint them, but it is difficult to get that hard, even finish without a paint booth. I don't think many contractors would paint new cabs on site, but others here may know differently.