Jan 26, 2018· A Bull Mastiff Labrador mix is going to be a big dog. Defining Characteristics of a Mastiff Lab Mix. Bullmastiffs have six colors and one marking recognized by the American Kennel Club. The colors are: Fawn, fawn/brindle, red, red/brindle, red/fawn and red/fawn/brindle. The recognized marking is a dark face mask.