Whoa! 4 weeks old?? That rather confuses me... My FBCM chicks were MUCH more feathered in by that time... On the upside, my FBCM boy had a significant comb at 4 weeks.
SO... I'm leaning towards pullet on this one although the feathering really throws me.
I hope it's a girl because one of my Black Copper Marans, that is also 4 week old, looks exactly like this. I actuall have two, but for one I am pretty certain that it's a boy because it has a big red comb at 4 weeks. However, as I said, the other looks exactly like yours.
I would have to go with pullet also. I have six at 4 weeks also. They have not feathered out either. Three of them have much larger and pink combs. The other three have similar combs like yours.