I want to give a small start help for color breeders, that are not firm in equine HEE genetics by now
First of all I would recommend to read those two threads in the genetics forum, to get a clue, what we are talking about:

Equine Genetics by Harle, who was the genetics queen
List of Genetic Profiles For Horse Colours by Reb, who did a wonderful work on this topic

For those, who do not want to read so much ( tough those threads are really, really important and informative )
I will give a short conclusion in an extra shortened version:

Homozygous versus Heterozygous:

Every horse in real life and at HEE has 2 let´s call it "gene-spots" for every color.
( in reality it´s way more complicated, but we don´t want to bother with those details atm )

When it is "produced", it gets exactly one gene from the Sire and one from the Dam.
It can not get any color, that neither Sire nor Dam have in their genetics.

A horse that has two copies of a gene is called homozygous. It will always give this gene to each of its foals.
A horse that has only one copy of a gene is called heterozygous. It has a chance of 50% to pass on the color to its foal.


For the examples here, I will take the Sabino pattern.
But it works the same way for every other dominant pattern, too.

small excursion to Harle:
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Inheritance
Think of a bully and a kid who gets picked on. Whenever the bully is around, the weaker kid is going to stay hidden. The only time the weaker kid will come out is when the bully is not around. The bully is the "dominant allele" while the weaker kid is the "recessive gene."

Dominant: This is a gene that is "stronger" than another. It can "hide" other genes. There only needs to be ONE copy of this gene in order to show up. Bay is an example of a dominant colour. Bay is dominant to black.

Recessive: This is a gene that is "weaker" as compared to another. It can "hide" behind other genes. A recessive gene will never show up in the presence of a dominant gene. Remember the bully. A completely recessive gene (one that is weaker than all the others that can be paired with it) can ONLY show up if there are TWO of it. Black is an example of a recessive colour. Black is recessive to bay.
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Back to my example:

So if you have e.g. a Sabino horse, but the Sire has no Sabino at all.
The horse will always have only one Sabino gene from its Dam and will have only a 50% chance to pass on its Sabino gene to its offsprings.
The shortcut for a heterozygous Sabino horse is: Sbsb

If you have e.g. a Sabino horse and both, Sire and Dam have the Sabino gene.
Then the horse can have either one or two Sabino genes, depending on the genetics of its parents.
In HEE, some experienced players can tell from the horse portraits, if the horses have either a homo- or heterozygous genetic.
If you are unsure, you will have to go to the vet office and do a gene test for that horse.
When the horse turns out to be homozygous - in this case with the shortcut SbSb - you have a 100% color producer for this kind of color gene.

You can breed this horse to any other horse - and each foal will be Sabino, too.
So if you see a horse without a gene test and look at its offsprings - and you will find not a single foal without Sabino, you can assume that it is homozygous for Sabino.


Mathematics for color breeders:

To make things more difficult, you have not only one parent for a horse, but always two - obviousely
So now it starts to get a bit more difficult. We learned already, that it gets exactly one gene from the Sire and one from the Dam.
You can get various combinations out of the 4 parents´ gene positions for every foal.


1) If you take a homozygous sabino stallion and breed him to a homozygous sabino mare you will always get a homozygous sabino foal.
in shortcut terms:

SbSb x SbSb = SbSb

2) If you take a homozygous sabino stallion and breed him to a heterozygous sabino mare you will get either a homozygous or a heterozygous sabino foal.
in shortcut terms:

SbSb x Sbsb = SbSb or SbSb or Sbsb or Sbsb = 50% chance for homo and 50% chance for hetero

3) If you take a heterozygous sabino stallion and breed him to a heterozygous sabino mare you will get either a homozygous or a heterozygous sabino or a plain foal.
in shortcut terms:

Sbsb x Sbsb = SbSb or Sbsb or Sbsb or sbsb = 25% chance for homo and 50% chance for hetero and 25% for plain color without sabino!

4) If you take a homozygous sabino stallion and breed him to a plain mare you will always get a heterozygous sabino foal.
in shortcut terms:

SbSb x sbsb = Sbsb = 100% chance for hetero

5) If you take a heterozygous sabino stallion and breed him to a plain mare you will get either a heterozygous sabino or a plain foal.
in shortcut terms:

Sbsb x sbsb = Sbsb or sbsb or sbsb or sbsb = 25% chance for homo and 75% chance for plain color without Sabino



Summery:

If you always want to get pretty colored foals, make sure your breeding stock has homozygous genetics.
Horses with a low color rarity ( even 1 of 1 ) are NO good color producers, if they do not have homozygous genetics.
They often have many patterns, but very seldom they are homozygous and will give you more plain foals than colored ones!


Usually you can start your color breeding lines better if you search for horses that are homozygous in more than one pattern.
Like you´d look for a homo Sabino & homo Splash White & homo Tobiano stallion ( even if he is "only" a 1 of 250 )
and breed them to a e.g. homo Rabicano & homo Silver & homo Tobiano mare

So the foals will always have Sabino + Slash White + Rabicano + Silver + Tobiano and a really rare color rating



I hope you were able to follow my confabulations and now you can post all your questions and I hope all the other color gurus in the game will help me with the answers

Notice:

If you have a foal like this:
edit: it seems the link to the foal is missing here:

It was a Tobiano Silver Brown Roan foal.

you do not have to gene test it.
The sire is Grey Tobiano Splash White Rabicano Appaloosa
The dam is Silver Brown Roan Dun

They parents do not share a color pattern, so the colt will be only heterozygous in the color pattern he has and not a good color producer at all

Thanks for this Kuwei!

Thanks for this! ItÂ’s very helpful.

Aussie Wattles said:
Thanks for this! ItÂ’s very helpful.

What breed would you say is a good one to do colour breeding with?

ISH, SH and PON have all patterns, so I find they are easier, while WB, X, TB, RID and AA can’t have the Lp complex (Appaloosa) but KNN have to have the Lp complex otherwise the foal is a SH and can never be a KNN. So I suggest ISH because you shall always get an ISH, no matter what other breed he/she is bred with. (Even though my fav is WB)

Willow Kiss Stables said:

What do you mean by "color pattern"? Sorry, I am new to this lol