I know this is a really old thread, but I am so glad I found it. I have 4 six week old RIR's and one started this pink coloring. I thought it was a rash, or some sort of allergy or irritation. I was afraid it was something she could spread to the others. I posted her pics Sunday on my state thread and everyone told me I had a cockerel. I was devastated as another girl started with some pink facial notes just last night as well.
I have been searching 6 wk pullet pics and found this along with some others that confirm this is just part of the aging and growing process. My first one to get the pink face has a pale yellow comb and all 4 combs are the same size and color still.
I hope your chick ended up being a pullet afterall! I am keeping my fingers crossed!