I have a 14 year old off the track Appendix gelding who has gotten spotted over the years. The spots started around when he was ten and he's just gotten more over time. The patchy white hairs are concentrated around his haunches and cheeks.

Here's some pics of Brewer (the spotty boy): https://imgbbpip.imgbb.com/

If you are interested, here is his parents (plus a record of his race failures): https://www.equibase.com/profiles/Results.cfm?type=Horse&refno=7956513&registry=Q

Possibilities:

Scarring from fungal infection

Really weird birdcatcher spots (that's what we've been calling him while we figure it out)

Let me know what color you think this is or what you think could cause this weird (but very pretty) coloring.

It's fungal scarring and sometimes what we thinks a bird catcher spot could also be scarring from something minor!

Jeez, they really raced him hard for a horse that wasn't placing well.

Has he had a fungal infection? If not, possibly vitiligo?

We just bought a horse with vitiligo. He only has one big spot and a couple smaller ones. Looks very similar to that.

He may have been a 'failure' on the track, but he sure is a stunner!