Saiph from Wait For The Jump asked several months ago what I use to keep Ashke looking soooo white. That question actually made me laugh outloud, because on most days he has several "pee or poo" spots from laying in his bedding at night. This is especially true during the winter.
So, to answer her question, I mostly just groom.
It is the activity that began my relationship with Ashke. I went out every night and pulled him from his stall and groomed him. He was so dirty. It took three or four baths before the encrusted crap that was permanently bonded to all of his hair came out. He was so dirty that it hurt him to use anything other than the softest curry and softest brush I could find. I went really slow. Once he had shed out the horrible hair he was covered in when I first brought him home, the grooming was much easier.
Now, two years later, his coat and hair look really good. His body color is mostly white with chestnut sprinkles. He still has his skull and crossbones on his hind left hock. I spend a great deal of time (most days) brushing and rubbing him before riding. He loves it still. He leans into the brush and lets me know when something is especially itchy. He loves it when I rub the long muscles in his butt. And along his neck and back. I go slow and pay attention, making it a moment of love and benediction, as much as a method of getting the crud off of him.
He gets rinsed after any ride that leaves him sweaty. He gets shampooed every couple of weeks or so, more frequently in the spring because of the mud and accummulated filth from the winter. I use the Vetrolin Brite White shampoo and it seems to work pretty well. I am also using a Eqyss Megatek Conditioner that seems to help thicken and soften his mane and tail. His mane is growing out much thicker and healthier than it has been since I got him, and at J's request, I am letting it.
This spring was his second "normal" shed and I haven't been as happy with his sleekness as I had hoped. After talking with Saiph and doing some research, I have added some Triple Crown Omega Max to his diet, hoping to speed his shed and improve the overall condition of his coat. So far, it seems to be working. We added it to Cali's diet as well, since she is itching the crest of her mane bad enough to leave a bald spot and the MTG seemed to be making it worse. He is dropping hair pretty good and beginning to slick up, which will leave him an almost gunmetal gray up close and when he gets sweaty.
So, there you go. I use lots of grooming and hand petting, great diet with supplements, and infrequent baths. It doesn't hurt that the majority of him is white enough that the camera "doesn't see" the greenish spots on his coat. He will be bathed on Saturday, after the clinic, and I'll be sure to take some pictures then.