Larger version is over on my art blog.

Ironically I did not like The Last Jedi at all, but the fathiers caught my imagination because I will glom on to any fantasy horse-adjacent creature you put in front of me no matter how weirdly utilized or poorly thought out it is. I've been reworking their visual design a little to make them less uncanny valley cgi and make them into something that fills the same aesthetic/cultural niche as a fancy sport horse, but it also bothered me that they were all the same color and not at all designed like a domestic animal even though they pretty clearly are. I get why they didn't spend time and budget on coloring them all uniquely for the approximately five minutes of screentime they had, but it was a waste of potential and also there's no way an animal bred entirely by ostentatious rich people with too much money and time on their hands doesn't have a robust community of color breeders and dubiously ethical halter lines and the general kind of fuckery you see with any animal that's been kept by humans for a while.

I primarily based their genetics on horses, but I also borrowed some from goats and sheep, took the piebald patterns mainly from deer, and made some of it up entirely (though outside the alchemy stuff I tried to keep everything plausible and cohesive). There are also genes horses have that fathiers don't, so it's not a direct 1:1 in either direction. This also isn't a comprehensive list of Every Possible Color Fathiers Come In, but rather all the color genes that can interact with each other in various ways. You can probably create some absolutely batshit-looking animals with this chart as well as very understated, mundane ones.

At some point I'll expand further on the very specific headcanons about ancient Sith and the history of fathiers overall that tie into all this (most of it is rooted in Old Republic era EU stuff since I don't really touch the disney-verse outside of stealing their creatures and I'm mainly in the SWTOR corner of the fandom), but that's one for my lore/oc blog. You can probably extrapolate the important bits just from reading through the chart if it interests you.