It is interesting to note that Brindle is not a color…it is a color PATTERN.  Yorkies must be able to make the pigment black or chocolate to “express” Brindle.  Brindle typically appears as black stripes on a red base.  Shades can vary from from light Brindle (mostly with red with black striping) to heavy Brindle (mostly black with some red), to black or “reverse” Brindle (almost entirely black).