How long for Marans to feather in?

I hatched a roo on April 1st from eggs that came from a BYCer's blue/black/splash Marans pen. He enormous already, and still filling in feathers. But so far I only see colored feathers on his neck. His saddle feathers are coming in nice and shiny, but solid black. His underparts look really dark blue instead of black, but I think they will end up black too.

Should he be showing more color now, is he still too young to have full coloring, or did I get a mutt?