It depends. Some of my ocs have very specific mane styles. But others just have a general style. When I describe my oc green, I just say he has messy or kinda spiky hair. But when I describe my oc mithril, I go into detail, because her mane is one of the things that makes her stand out.
Yes, because the mane should be a color that looks nice with the coat color. So, for example my OC, Claze, has a red mane with purple streaks because her coat is blue, and her hair was originally only red, so red+blue= purple, and decided to add purple streaks in the red hair.. Another example, Claze has red eyes which start to crackle like fire when she becomes pissed (angry ) since her mane is red, and fire is usually red, but sometimes blue. o3o