Don, I have someplace a bunch of photos of the shirts we can do, but first of all I'll mention that we aren't "painting" the colors on the shirt but rather dyeing the fabric with color. That's a good thing because the "paint" - a/k/a silk screen ink - can wear and flake off. The dye is heated to a gas that permanently colors the fabric.
But -- when dyeing the base color of the item (shirt) doesn't change. So, for instance, if I tried dyeing a red shirt with red dye -- you wouldn't see much at all. If I tried dyeing a red shirt with blue -- you'd get a grungy looking brown or something. And so on. A dark grey shirt would work - sort of - because we'd start with a dark fabric that can only get darker with the addition of a dye. While there are (supposedly) new methods and inks available to dye dark fabric, we haven't tried any of them so can't offer the process - nor even say how well it might work. As for bleeding -- no, that doesn't happen much at all with our process.
And there aren't any white dyes, either, until you're getting into those same kind of brand new products with which we don't have the techniques yet. White shirts do they best in our process. I'm at the house now, but will look at the vendor's catalog tomorrow to see what's what. I know they offer some colored shirts, and if so -- maybe they've got recommendations on how to dye those dark shirts. I'll let you know. In the meantime, here's this year's Salt Talks shirt. This is the first shirt we did -- might not have all of the color balance correct yet. But it's the only photo I've got here. You can see, though, that we can do a full spectrum of colors, not the few that silk screens are limited to using. They do three or four or five basics and can sort of overprint one with another to get a third shade, but only to a certain extent. No limits with ours. And by the way -- we use polyester fabric. The more polyester the better. 100% is great, 50% is acceptable if that's the best you can find, and much less than that won't work worth a durn. Under Armour is 100% polyester.