I'm not an expert on 'colors' but your roo could of come from the blue gene and passed it on to its offspring. There was just enough of a hens gene color to combine with the Roos and make a blue chick! I would call the roo "black" or "blue". Where did you get your roo?
No they are full breeds. I do have 1 roo crossd with a dutch bantam and silkie just to see what they would look like. All my silkies are pure in there own coop