I have a white Delaware hen that has exactly this, I first noticed it maybe about 8 months ago. Like I said, dont let the red color bother you too much, I found that that area is really profused.
I think my hens is caused by chronic poopy butt which Im learning seems to be caused by a lot of things. She is my only hen that has this chronically.
The seems to be the poopy butt irritates that area, poop sticks to the skin. It could be her pulling her feathers out trying to get herself comfortable, or the feathers are falling out, or others are picking them out.
So since its started Ive tried to ID the source of the poopy butt. Heat, changes in weather, too much water seems to cause it. Scratch grain really causes it, the corn. Also, rebrascora has a really good theory that fatter hens get chronic poopy butt as being fatter changes the structure of their vent position, and it might be this too, and shes top of pecking order, and she is a little portly, so Ive been trying to keep her weight down.
I also give her a bath about once a month to get the stuck on pieces off. The bath also helps not expose that area to being pecked. Recently its been better.
In addition, the area could have been feather picked when she was roosting but she is top of pecking order...I never saw it but it could have happened.
But it is all healed now, there are still a few feathers to grow in but much better. The feathers took forever to grow back in.