I'm with the MTG as well, although I've heard really good things about Eqyss for rainrot as well. I've used MTG on my dark bay with no color change, and I've also used the Eqyss moisturizing shampoo for his itchy bum, which worked very well.
Some horses just change color when they shed every year. We have an appy/arab who goes anywhere from a pale gold to golden to a brown golden when his sheds his winter coat, which is white!
"Sit tall in the saddle, hold your head up high. Keep your eyes fixed where the trail meets the sky. And live like you ain't afraid to die...don't be scared, jut enjoy the ride." - Chris LeDoux