Over the course of many generations, horses have been used and bred for work and meat by humans. A third important factor sometimes contributing to a horse's value, is colour. For a long time, breeding for colour has been just as elusive as breeding for performance. The fiasco of the hanoverian creams in European history is a clear example.
These days, breeding for (or against) a particular colour has become more straightforward. Not only are we better capable at identifying the colour itself, but scientific research has discovered many of the underlying genetic causes, and created DNA tests that can verify if they are present. Still, much of the terrain is still undiscovered, leaving enough to make us guess.
The most important part of understanding horse coat colours, is understanding the possible base colours . These are black, chestnut, and bay. The first two are caused by a gene called extension, the third by agouti.