I agree, not a deal breaker, but if you buy the horse, be aware you should take some extra steps to keep him protected from the sun (some options are long-nose fly masks, sunscreen, or night turnout).
There are also some plants (buttercups and some types of clover, for example) that can make horses photosensitive, and it could be that if the horse doesn't have access to those wherever you keep him, it may not be an issue at all.
“The horse is a mirror to your soul. Sometimes you might not like what you see. Sometimes you will.” - Buck Brannaman
"Nothing forced can ever be beautiful." - Xenophon