A lot of people ask questions about how rerolls will change their horse's coat color. I figured I'd make up a quick list of the various color changes that may occur. Genetics will never change; pattern, marking and coat color variations may change.
Chestnut - with roans and duns, this is called Red
Flaxen chestnut - with roans and duns, this is called Flaxen Red
Liver chestnut - with roans and duns, this is called Dark Red
Flaxen liver chestnut - with roans and duns, this is called Flaxen Dark Red
Rerolls may also add or take away coat modifiers such as sooty (dark hairs) and pangere (light hairs). These are not represented by genes, but you can see for sure if your horse has or does not have them with a gene test. They are listed under Phenotype at the bottom of the test results. Like the coat color variations, they are random and are not inherited or passed on.
Brindle will always stay, but may change color from black to white, or vice versa. This is also not inheritable or passed on. Rerolling your horse will not add brindle if it does not already have it.
Markings such as socks, blazes, etc may change or disappear.
Patterns such as tobiano, frame, etc may change in variation, but will never disappear, as they are genes. Rerolling your horse will not add a pattern(s) if it doesn't already have it.
Additional markings such as bend-or spots, bird catcher spots, lace and chimera may come and go randomly with rerolls. These are not genes and are not inheritable or passed on.
07/08/18 - Edited to add Chimera.