The Foundations: I find that the easiest way to think about horse color is to imagine it as a series of building blocks. Each color is built from a group of genes that act differently when combined with different bases. One key thing to understand is that horses inherit color genes from each parent---each parent has several pairs of color genes, and half of each pair is passed on to the foal. If you are not familiar with basic Mendelian inheritance, please read this wiki page for more information.

All horse colors are built on only two base colors, black (E) and chestnut (e). Black is dominant to chestnut, and chestnut is thus recessive. That means that a horse carrying 2 black genes (EE) will be (homozygous) black; a horse carrying one black gene and one chestnut gene (Ee) will also be black (but heterozygous); and a horse carrying two chestnut genes (ee) will be chestnut (always homozygous). So if two heterozygous black horses are bred together (Ee +Ee), they have 1 chance in 4 of producing a homozygous black (EE), 2 chances in 4 of producing a heterozygous black (Ee), and 1 chance in 4 of producing a chestnut. Pretty neat, huh? Two chestnuts bred together (ee + ee) can only produce chestnut.

Chestnuts vary in shade in from a light golden red color to coppery red to dark liver. Some of the darkest liver chestnuts, often called "black chestnuts," are nearly indistinguishable from true black horses. Some chestnuts have have flaxen manes and tails. Burgundy Sun, an Arabian owned by Phara Farm, is a stunning example of a flaxen black chestnut.