Basics to Genetics
Base coats and how they transfer to a foal;
Realistically horses coats usually come out in a nice even pattern or color. Our base coat colors are Black, Bay, and Chesnut. Each one of these colors can be diluted, to different variations.
If horse A and B breed, what will the foal look like?
Good question. Assuming your horse has a line behind it, the past genetics of the lineage will benefactor the upcoming offspring. Assuming you have a line full of (Aa ee) chestnuts and (ee Cc)palomino's on the fathers side, and a line full of (Aa Ee)bays, and (Ee) blacks on the mothers side, the chances vary. Horse A will be the father, horse B, the mother. Or Sire and Dam. Horse A is a (Aa ee)chestnut, horse B is a (Aa Ee)bay. If these two cross there's a likely chance that the horse will be a chestnut, or bay. I would route more for the bay, as catching the Ee would be fairly easy with a chestnut sire. Any other color will be the tiniest chance. This also depends on the horses alleles. None of this exists in the sims though.
Regarding sim horses, if you cross a chestnut and bay, the horse should come out a SOLID color, no abnormal markings should be displayed. If any do show up I advise you edit them off for a more realistic outcome.
When a horse is diluted with one dose of the cream gene ee Cc, from say a chestnut, the horse will be a palomino. If a bay horse is diluted with one dose of the cream gene Aa Cc, the horse will become a buckskin. If a black horse is diluted with one dose of the creme gene, Ee Cc, the horse will become a smoky black.
This example is from a real breeding.
The sire is a buckskin, Aa Ee Cc, the dam is a chestnut, Aa ee, The chances are very likely to get another chestnut, or a bay, however it's also possible to get a palomino. This pair did produce a palomino, Aa ee Cc. Which is less likely to happen, but it did!
Now we enter the world of patterns, which can be placed over virtually any color. Even white, although you cannot see it. Common patterns are Tobiano(Tt), Overo's(Oo), Tovero's(TO), and Leopard(LL). If leopard is heterozygous(Ll) you get a blanket.
Assuming you try to breed any TT or OO horse, no matter what that horses offspring will be a Tobiano or Overo. If you crossed an Overo(Oo) with a tobiano(TT), you have a chance of getting a tover(TO) which is one copy of both tobiano and overo. That foal will now have a chance of producing either tobiano or overo.
A Leopard(LL) with another leopard(LL) will give you a leopard. A leopard(LL) with a Blanket(Ll) will give you a chance at a blanket or a Leopard.
COLORS are awesome.
ee aa gg ff dd tt oo rr ss ll zz cc chch
This is not is order, and I'm missing some most likely, but those are basically all the fun colors in a horse(simplified).
I'm not going into incredible depth, but just what's what.
Agouti-What makes a Bay (Ee Aa)
What makes a chestnut (Aa ee)
What makes a Black (Aa Ee EE)
What makes a grey (Gg GG)
What makes a Dun (Dd DD)
What makes a Tobiano (Tt TT)
What makes an Overo (Oo)
What makes a Roan (RR Rr)
What makes a Sabino (Ss SS)
What makes a Leopard (LL)
What makes a blanket (Ll)
What makes a Silver (Zz ZZ)
What makes a Cream (CC Cc)
What makes a Champagne (CHch CHCH)
Flaxen Gene(FF Ff)