The minifig scale dog has only been made in 2 colors--new dark gray and new brown.  LEGO presumably started making the dog piece to be The Grim in the Harry Potter sets, because the dog piece first showed up in 2 Harry Potter sets in 2004.  In the movie (and maybe the book too; I don't know), the Grim dog was dark gray or black.  ...

The minifig scale dog has only been made in 2 colors--new dark gray and new brown.  LEGO presumably started making the dog piece to be The Grim in the Harry Potter sets, because the dog piece first showed up in 2 Harry Potter sets in 2004.  In the movie (and maybe the book too; I don't know), the Grim dog was dark gray or black.  ...