Does the Landseer or English Mastiff have a limited range of colors? 
Landseer (dog):  It is not to be confused with a white and black Newfoundland, which is also often called a "landseer". English Mastiff: The English Mastiff is a breed of extremely large dog (often known simply as the Mastiff) perhaps descended from the ancient Alaunt and Pugnaces Britanniae, with a significant input from the Alpine Mastiff in the 19th century. English Mastiff:  Distinguishable by enormous size, massive head, and a limited range of colours, but always displaying a black mask, the Mastiff is noted for its gentle and loving nature.
English Mastiff