I don't see anything that would make me think it's not a marans, but it is definitely blue and not black.
As to gender, with the size and redness of the comb a wattles at six weeks I would strongly suspect male. However, single combed pullets can sometimes develop fairly large combs early on, so I wouldn't say I'm 100% certain this chick is a cockerel. Keep an eye out for pointy saddle feathers coming in around 9 weeks or sounds of strangled crowing.
As to gender, with the size and redness of the comb a wattles at six weeks I would strongly suspect male. However, single combed pullets can sometimes develop fairly large combs early on, so I wouldn't say I'm 100% certain this chick is a cockerel. Keep an eye out for pointy saddle feathers coming in around 9 weeks or sounds of strangled crowing.