Darkening vagina?

OK so I have a weird question.. I feel like I'm going crazy here. it's ovulation week so I've been trying to track my CM but there really hasn't been any and today I noticed the vulva looks to be a bluish brown color when it's usually pretty pink?? anybody else have this happen? I'm STD free and so is my boyfriend. could this be a symptom of something? I'm starting to freak out. help!!