sleeping your guinea has pink skin and now that I'm looking after sows (after years of boars) I appreciate just how much they pee. Much, much more than the boars.
Also, when it's this time of year, they are less active. My girls have layer of woodbased cat litter (like long thin pellets, it is recommended as small animal friendly) in their indoor cage with newspaper and a fleece (I have stopped giving loose hay indoors, I never stopped hoovering it, they have the hay cookies inside)
Outdoors, newspaper and hay. I know from the lack of evidence (no poohs) outside their haybox that they don't actually do much.
So YY , they are prone to sitting in their pee.
It's a bit like pressure areas when people are immobile. If you can't get them moving, you need to protect them.
My ladies have a mixture of foot colours, GP5 is mainly brown (odd pink toe) GP4 has black/pink.
We noticed that our boar got pinky feet when he wasn't well, because he was static, very unlike him. He spent his whole time patrolling.
If you do use fleece, make sure you have something absorbant, like newspaper underneath, it's designed to 'wick' away moisture.
And be careful with detergents, some will irritate their skin.
Good Luck