Modifiers Overview
Every horse has an underlying base color of Black, Bay, or Chestnut. However, certain genes can modify the appearance of these colors without changing the horse's underlying genetic base. These are known as modifiers.
Modifiers can affect a horse's coat in several ways, including darkening or lightening certain areas, changing the distribution of pigmentation, or causing the coat to change as the horse ages.
Unlike dilutions, which primarily reduce pigmentation and typically lighten the horses coat color, modifiers can produce a wider range of effects depending on the gene involved.
How Modifiers Affect Base Colors
Just because two horses carry the same modifier doesn't mean they will look identical.
For example, the Sooty modifier can cause a horse's coat to appear darker, sometimes producing deep liver chestnut shades or darker bay coats. In game, there are multiple sooty overlays saved at different opacities, so two horses that both carry sooty and are genetically the same may look slightly different.
Other modifiers, such as Flaxen, primarily affect the mane and tail, producing lighter hair on chestnut based horses.
Grey is another example of a modifier, causing a horse's coat to progressively lose pigmentation as it ages, once a horse reaches approximately 15 years of age in game it will have lost the large majority of it's pigmentation to the point where you can no longer reliably distinguish the original base color or markings.
Modifiers do not change a horse's underlying base color. A horse that appears grey, for example, still carries its original Black, Bay, or Chestnut genetics, which can be passed down to its offspring. Just because it is not visually displayed, doesn't mean that the horse does not carry a certain genetic.
Modifier Inheritance
Like other genetic traits, modifiers can be dominant or recessive depending on the gene involved.
Some modifiers only require one copy to visibly affect the horse's appearance, while others require two copies like Flaxen.
Some modifiers are only visibly expressed on certain base colors. For example, Flaxen only affects horses with a chestnut base, meaning a horse carrying Flaxen on a Black or Bay base color may not visibly display the trait.
However, the horse can still pass the genetics down to its offspring, potentially producing foals that visibly express the modifier depending on the pairing.
Combining Multiple Modifiers
It's also possible for a horse to inherit multiple modifiers, which can interact with each other to produce different coat appearances.
For example, a horse may inherit both Sooty and Grey, resulting in a darker coat earlier in game that then lightens as it ages.
Modifiers can also interact with dilution genes and white patterns, creating even more variations in coat color.
Because of these interactions, two horses with the same base color can look completely different depending on the additional genetics they inherit. Some horses may not look anything like their original base color.