Brindle is a common coat pattern among dogs (as well as other animals). An easy way to determine if a dog has brindle coloring is to look for the appearance of stripes on the coat. Most of the time the stripes will be a darker color than the coat's base color.
The majority of breeds will have brindle coloring across the majority of their coat with an occasional patch of white fur sometimes appearing on the chest, paw, or muzzle. Other breeds such as the Bulldog and Bull Terrier will have white coats with patches of brindle appearing on their face or on their torso.
What Causes Brindle Coloring
Brindle coloring is a genetic trait where some of the hair follicles express different alleles. This results in pigmentation that gives the appearance of stripes on top of the base coat. Despite brindle being genetic, it is very difficult to to test for making it unlikely for breeders to determine if future offspring will have brindle coats.