I always used Quic Color on my bay. It intensifies natural coloring, perhaps you could try it on your paint? I also love Cowboy Magic products. They make excellent detanglers and stain removers for the coat.
I would be careful when using "human" shampoos, they often are so drying and make the animal itch/rub. (It's such a sad day when a horse rubs out their beautiful tail.)
For show season or just to show off, baby powder intensifies white areas or markings. It looks great. I have also used baby oil on the mane or tail to create more of a shine. I try to avoid the hair folicles, just coating the hair. World Champion Pepi Show Sheen is amazing and recommended to me by a professional. It can be used on the mane and tail as well as the coat. I own a grooming mit that puts shine back into the coat quite well. They make wool and sheepskin. I don't wash it as to keep the natural oils in the mit.
I have also heard apple cider vinegar is amazing. I have been recommended feeding 2-4 oz a day or diluting it with water and using it to wash with. It makes the coat healthy, shiney and keeps flies away.
Hope that helps a bit. =)