There are quite a number of resources on the internet for horse colors and the complicated genetics behind them.  Since this information is known to change from time to time I will not attempt to duplicate the information here, but will leave it to the experts.  Below are a few links to sites which we found useful on horse colors.  We hope you enjoy them as well.

www.equinecolor.com

http://www.equusite.com/articles/basics/basicsColors.shtml

http://www.vgl.ucdavis.edu/%7Elvmillon/default.htm

http://www.apha.com/breed/geneticeq2.html