So Sprinkles' grays in her hoof are going to more green or pink or blue, because the dark coloring isn't "true" black...
This got me to thinking about the variation in tone on Sprinkle's hoof, and how different they are from Freckles, another appaloosa that shares a pasture with her (above). While the two horses were standing together, what struck me was how opaque Sprinkles feet were compared to Freckles. Shell hooves have always seemed to me to have a slightly translucent quality, and the other mare's feet retained a bit of that.
I wonder if this is just individual variation, or if base color might have something to do with it. Looking at the picture above, Sprinkles and Freckles might both appear to be chestnuts - one a darker liver and the other a true red chestnut. The truth is I am not sure if Sprinkles is genetically chestnut or black. The general rule of thumb is that faded black horses retain their black lower legs, so if the lower leg is faded the horse is most likely dark chestnut.
Sprinkles lower legs are faded, which should mean that she isn't black. But the leopard complex gene will often change black base colors to an odd bronze shade that most horsemen find hard to categorize. People around Sprinkles have that problem, not knowing whether to call her black, or chocolate, or grulla. (Grulla seems to be a used as a catch-all phrase by many horsemen, meaning "dark, dull color I cannot identify".) To give an idea of just how dramatically the appaloosa gene can distort the color of a black horse, I'll share a picture of another appaloosa that tested as genetically black.
(I apologize that this is not my photo, nor do I know its source. If it is yours and you would like it removed, please let me know and I will do so.)
All this gave me the final push to have UC Davis test Sprinkles. I have meant to do this for some time now, but at last I have sent the form with her hairs. I still don't know, as Mel mentioned, if there is any true black in nature, but at least I will soon know if I own a truly black horse! And in the meantime, I hope to collect more pictures of appaloosa hooves and see if the striping differs according to base colors.