The one on the right here is the one in question. The one on the left is the previously identified roo. Below they are on opposite sides in the next couple of pictures.
They are six weeks old now and a couple of weeks ago I thought their combs were both turning pink and then red....then one stopped. Smaller comb, lighter and the bird is bigger.
Last photo one on my left is pullet and one on right is cockerel so far. I think it is too early to be certain - another two weeks would be a better time to ask. They aren't showing hackle feathers yet - just chick down. If pointy feathers come in - that's your cockerel.