I've been keeping my eye out on this one for a while. I have two younger chicks that are redder and are pretty obvious roos but this one still has me guessing. The one I'm wondering about is the silver laced cochin mix..the larger speckled chicken in the first pic which is the main chick in the second one.
looks like a girl to me but you should watch it and see if it acts like the other roosters. there is another trick... if you tie a magnet to a sting and hold it over the chickens back and NOT moving it at all if the magnet swings its self in a circle then its a girl if it swings in a strait line its a boy. I've tried it before but i don't know what makes this happen or if its 100% right or not but hey its worth a shot!