Hi Nicol, sorry I didn't reply to your question, been insane around here for a week. Yes, you can sex wheatons at hatch by color. Stags will be reddish and pullets lighter, even yellow, or white. To help with the pasty butt issue, a small amount of molasses in their water (mix to look like weak tea) for one day will cure it. Pasty butt, believe it or not, is a symptom of constipation. What happens is, the white stuff (urine) gets by the blockage and cannot escape quickly enough to keep the vent clean. Molasses is a natural laxative for fowl and will clear it up. There are several causes for pasty butt, stress, high incubator heat, etc. so ya hafta sort it out to see what is causing it.
Nice chick. Strong legs. Most likely a pullet. Good luck with them.......Pop