Also, and this is something I am dealing with now with my Grade Paint is to be aware of photo-sensitivity if horse is pastured. Kola this year, and I've had him since 2000 (?) at least, and no problems ever, but he got orange nose and cheeks, and a strange hair coat, almost like the sand at beach when waves come up and leave ripples in it. Really brittle too.
Took him to vet, and first thing he said was photo-sensitivity, and the color and coat was liver damage. He is better, but will have to be more or less on dry lot now, and best if out of sun, only out at night, and grain and hay, as don't know what he got into.
He also this year seemed to sunburn worse than ever before, around eyes too, which vet said can be a warning that horse is having problems with something they are grazing on and the sunlight.
Horses make me a better person.