Sudden darker coloration

This is my beetle Darcie, over the course of about 10 days her coloration around her head has darkened. The first picture is from tonight, whereas the second one is from about 10 days ago.

She used to come out almost every single night from a log hide she likes to rest in, but for the past 2 or so weeks she's been unusually dormant, and has come out once to eat. Temperature hasn't changed, feeding schedule hasn't changed since I got her (a year and a half ago), and I always wash their (2 other tank mates, black and smooth dfb) food properly.

Is it age, or maybe the wax rubbed off her head on accident? I find the latter harder to believe since she's been under the log for quite some time, moving around a tiny bit but staying under it. Any insight is appreciated.