Dilution gene is a popular term for any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:

Albinism describes a condition where there is no color pigment

Equine coat color describes various colors in horses

White (horse) describes the unique genetic processes that create truly white, not diluted, color in horses

Gray (horse) explains the process of the gray gene, which lightens the coat over time, but is not a dilution gene

Dun gene describes another common dilution gene in horses

Champagne gene, describes a different and rare dilution gene in horses that also creates cream coloring.

Leucism describes a condition that creates loss of pigment

Silver dapple gene, describes a dilution gene that works in a unique manner, lighting the mane and tail of a horse to a greater degree than the body color (opposite of most dilution genes, which act more strongly on the body color)

Cat coat genetics discusses many dilution genes in cats

Equine coat color genetics discusses color genes in horses, including a brief description of dilution genes

Cream gene, describes the process for horses by which the cremello and perlino colors are created as well as the buckskin and palomino colors