I bought my chicks out of the pullet bin, so I'm hoping to confirm they are all females. They are 7 1/2 weeks old and they all look pretty much developmentally the same to me, with some having a bit more or less wattle. They all have fairly red combs. Here's some pics.
I thought I would add a few more photos of the one I'm worried about. She's of course my favorite and the only one who likes to sit on my lap and be pet. I'll still keep her if she's a he, but I like hearing what people with more experience have to say. Oh and she's a bit over 8 weeks now.