Welsummer chicks

I was given 6 welsummer eggs to incubate, all eggs were deep mahogany brown, 4 hatched out but i thought they should all be the same colour, this is not the case, 2 are yellow and 2 are brown, although the yellow ones are getting darker wing feathers, would these be males, or could they be x breeds :?:

a mix up im thinking , birds often slip into a broody hens nest and lay a couple rogues