I also have a cremello horse, though I am lucky in that he doesn't seem to like getting dirty... except when I take him to shows. :eyeroll: At that point, he likes to poo in the middle of his stall and sleep in it.
I use Cowboy Magic Green Spot Remover on my horse's knees and hocks once or twice a week. Otherwise, he gets permanently stained there.
Before I go to the show, I bathe my horse with EZ All, mostly because it's really easy to use and smells great. The problem with pink skinned horses is that when they're wet, you can REALLY see how dirty they are. I'm sure the shampoo helps loosen up the dirt, but what really does the trick is a hose with a fairly high pressure nozzle (mine has a flat "fan" shape that does a really good job). It's kind of cool to see all that dirt wash off...
For the "fresh" stains he gets at the show, regular shampoo (currently using Gallop brand shampoo) and a scrubby glove works fine in getting it out. I've tried using Cowboy Magic Green Spot Remover for these, but I wasn't really happy with the results, especially on the larger spots.