Kitten's anus is bright red

I adopted two six month old kittens about a week ago, and I have noticed that one has a bright red anus. 

She is behaving normally and is eating both wet and dry food. She has been dewormed. She does not appear to have diarrhea; her poops look completely normal. She doesn't appear to be in any pain; she's active and is playing normally. 

I'll be calling the vet on Monday, but does anyone have any advice?

Thanks so much.

I would be doing as you are already doing and talk to my vet if I was concerned. She is probably fine since all else is normal, ie stools and all, but never hurts to ask.

 Has she had any constipation or hard stools?    It's possible she might have some irritation from that leading to swollen , inflamed tissue, maybe an anal prolapse.  (not as bad as a rectal prolapse or colon prolapse ) 

There's some ointment you can get from the vet that eases the inflammation. 

  I  had a kitten who occasionally had that problem starting at 4 months, and I found that switching him entirely to wet food helped.    He never had it again after about 8 or 9 months old.

There is not a red donut or sausage like thing noticeably sticking out, is there?    If so,  you need to get to the vet Monday AM , and until then make sure to keep that tissue moist.   But I think you would have described it differently if you were seeing something like that-- it would look more alarming.

This response is late, but here's an update:

About three hours after I made the initial post, I noticed that the kitten's anus had gone completely back to normal. I took her to the vet anyway, and it turns out that she has a minor rectal prolapse; it's more noticeable after her bowel movements (which are normal, no diarrhea or anything like that). The vet thinks that she'll outgrow it, but I've been keeping an eye on it anyway. The kitten seems to be doing normal.