The agouti signaling protein gene (often shortened to agouti or ASIP) controls where black pigment is produced on the horse.
The black/red factor test (also known as “extension”) determines the underlying base color of a horse in the absence of any modifiers (such as agouti).
Incontinentia pigmenti (IP) is a variant of the IKBKG gene on the X chromosome, causing in weepy skin lesions present at birth.
Champagne is a variant of SLC36A1 that reduces the amount of both black and red pigments.
Dominant white (“W”) refers to a class of white spotting patterns in which a horse with one copy generally displays markings on 50-100% of the body.