Horse Color Genetics: Gray

So now you have the basics down! Review: E = black, A=bay.
If all horses are really chestnut with different colors added on, then how do you explain white horses?
For white horses, it is important to understand that white horses are not really white at all. When people refer to 'gray' horses, this usually means a horse that looks white, but in fact their skin is a different color.
Gray horses are born a different color (usually dark bay or black), but inherit a gene from one of their parents that causes them to turn white (or the technical term is gray) as they get older. The gray gene is a dominant one, meaning that if any horse is  heterozygous or homozygous dominant (one or both genes being dominant) it will effect any color horse the same way.
Truly white horses are really, really rare and actually are born white. That is a different topic, but horses born pure white are called 'dominant white'.
The symbol for gray is G; any color horse who inherits either one or two of these genes will turn white, no matter the color. Here is a gray horse:

Again, even with grays, the trait can be either homozygous or heterozygous. If they are heterozygous, then their foal may or may not turn gray with age, there isn't really any way to tell right away unless you test them genetically.
Some gray horses don't turn white all the way; some remain in a state in-between. This color is referred to as 'dapple gray'. It is a color, but they still carry the gray gene. Their genetic code is still the same, or they may still turn lighter, or they could stay like this forever. The amount of graying cannot be determined.

Here is an example of a gray horse's color code: Ee, aa, GG (I'm just making this one up). This horse was born black (I know it was black and not bay because both of the a's are recessive), but will most certainly gray in time because it inherited dominant gray genes. And because this horse is homozygous gray, it's children will most certainly gray as well. You only need one dominant gene for the gray effect to happen. Another code is Ee, AA, Gg. This horse was a bay, but will gray in time. You see? Gray is a more simple concept to understand compared to some of the others.
Sometimes gray horses that turn pretty light will develop little tiny flecks that look like freckles. They can be all over the body, fairly large flecks, or in just one area. This is called 'flea bitten gray'. It is not a genetic thing that can be inherited, it just happens. The color of the flecks depends on what color they were before they turned gray. Black horses turned gray that develop flecks will probably have grayish flecks, while the horse below might have been chestnut or bay because they are brown.