Which color fleece has been the least treated?

I do dressage and I have a dappled gray westphalian warmblood with very sensitive skin. He had some sort of irritation, we assume caused by the girth, that had to be surgically removed. I had used a black fleeceworks girth cover, but it turns his hair bright pink from the dye and the vet said that he'd be better off with a white one that's less dyed. Are white ones less treated or cream colored ones?