The "blue" coloration comes from the American Staffordshire Terrior which was bred to the APBT for larger size and more legs all for the looks purposes. Thus is why most blues are over 50#s and not the 40# game dogs. This is also why a "blue" dog typically is not GAME.
After saying this my top male is CD is blue and my best female is blue fawn, but I like a 60# lock it down full of heart pit and these can be found in any color.