This is just a summary of the most important color genetics for me to look up quickly when generating a foal! For detailed information, I recommend JNFerrigno (https://www.deviantart.com/jnferrigno)'s journal about Equine Coat Colors and Genetics: http://jnferrigno.deviantart.com/journal/20437071/ !
Base Colors
There are two different pigments in mammalian genetics:
Phaeomelanin - a red pigment
Eumelanin - a black pigment
Since black is darker then red, phaeomelanin is covered by eumelanin, when both pigments are fully expressed.
Without dilutions and other modifiers, there are two base colors that are the result of the two pigments:
Black and Chestnut
E -> creates bla