I had some cochin bantams that I thought 4/5 were roos, but around 6 wks the 3 roos combs got much redder and bigger than the one pullet that had a fairly large pink comb, it didn't grow more or get redder and the feathering is different. I would give it a little more time. The one that 1 am sure is a pullet still has a very small and pale comb.