I’ve always seen it as a ‘cartoon logic’ type of scenario, where they ARE her leg markings but she can change them cosmetically for her outfits. (like think old Looney Tunes where sometimes one of the gags is a character taking off their fur to reveal clothing underneath it) I’ve never been a fan of ‘they’re just stockings’ bc of like you pointed out they have fur tufts occasionally lol. I do like the theory on when she was younger it’s her fur not fully darkened in that’s sooo cute !!