Oh, there could also be albino, with the Castor x Chinchilla cross if the buck has the recessive 'c', I hadn't noticed that I'd forgotten the albino option the other day.
We have very little coat problems such as caked up bums, but we've been breeding them for low maintenance coats for a long time now.
I did try a crossing between different breeds of angora (pure English to a Satin/German hybrid) and even though the offspring had the long wool, they lost the proper coat structure so all they did was mat up. A proper angora coat doesn't mat as much as many folks think it should. The purebred English lines that I have also molt (some lines have been bred to not molt, mostly for the show bunnies) so even if they do mat, they will molt the mat off. Most times, anyway, although not always. I've gotten rid of all the hybrids except one doe who's just a 'wooler' and not a breeder. She's third generation from the hybrid cross so she keeps her coat somewhat tidy but still gets mats behind her ears as well as a few other mats here and there.
The buns here are also kept in wire bottomed hutches so everything falls through and doesn't stick around. So I guess how we keep them clean is purebreds on wire? They get a lot of roughage in their diet, too, so that should keep things in pellet form instead of anything soft and mushy.