Zafur: It might actually be best to drop the ita and swap it with an -a like suggested and stick to surpentra/makulta.

Perhaps there is a need to specify the coat to eliminate the confusion?
Something like this, perhpas?: "Mi vidis surpentritfelan cxevalon."

I reckon I agree, but a problem with specifying the coat bit, especially with "surprentritfelan" is that our horse just got a whole lot of syllables forced upon it

Might just be easy to say "amerika makula/mikskolora ĉevalo" since the adjectives and word boundaries are more visible and easier to distinguish.

ceigered:

Zafur: It might actually be best to drop the ita and swap it with an -a like suggested and stick to surpentra/makulta.

Perhaps there is a need to specify the coat to eliminate the confusion?
Something like this, perhpas?: "Mi vidis surpentritfelan cxevalon."

I reckon I agree, but a problem with specifying the coat bit, especially with "surprentritfelan" is that our horse just got a whole lot of syllables forced upon it

Might just be easy to say "amerika makula/mikskolora ĉevalo" since the adjectives and word boundaries are more visible and easier to distinguish.

Yeah... it's probably best to leave "painted X" as "mikskolora X" rather than trying to get the nuance of "painted". Unless there's a specific need to specify the kind of mixed coat. (paint, merle, brindle, speckled, etc)
Such as being outright asked:
"Mi havas mikskoloran cxevalon."
"Kia mikskolora felo?"
"Surpentrafela."
(Or perhaps just surpentra, surpentra, etc, because the meaning is much more obvious...)

This would leave the longer form much rarer, only used in situations where it'd be preferred to give complete info upfront. I can only think of situations such as selling, where you'd want your customers to know what kind of coat your animal has upfront.

@ Zafur, that works in my mind. I don't think we can really get much more specific

Maybe if horses become a big thing in EO culture though, we'd start to see more and more universally accepted vocab for these sorts of situations, but for now I think what you've got is pretty much as good as we can get.