It is not all that usual for Fav chicks to get some kind of "smuttiness" in the primary wing feathers. Some would be darker and other would be lighter. The regular Salmon girls do get a little darker smuttiness than the Blue Salmon girls which they would be a lighter grey in color. I agree with the others, wait a couple of weeks to get the upper part of the wing colors to come in and then you would be determined which sex it would be.
If they are hatchery bred birds, they can go either way but the sticking point would be are the chest feathers and leg feathers. If Black or blue, its a roo. If pale salmon creme color, its a girl. If it is brown, then it MAY be girls. Hatchery Favs are the worst kind of example of the world of Faverolles. If you want the "real" thing, go to a breeder!