Has your Lona been pregnant recently? I believe that if they're darkened, you've recently had a baby or more. Not 100% sure since I only do the pregnancy content when I'm prepping for rebirth to update.
After a bit more snooping (and a rebirth), I think I know what happened. While darkening might also be related to recent births, what I was seeing was the effect for pubic and anal hair growth (which is odd because I had neither state at the time).
I am guessing this is a bug, but you can fix it by adding the state(s) (note you need to do it twice for it to show), shaving all via self-care skill, then removing the state to prevent more growth in the future.
Might be I added it in at one point out of curiosity, and the dev didn't disable the overlay darkening increment with the state being lost (a reasonable assumption since you aren't supposed to lost or gain it except at rebirth).