Ok, well I had this happen to me after a couple electro rounds on the upper lip. Directly afterward and after healing things looked great, but after about a week I started to notice this greyish almost beard shadow look going on, and it was very hard to hide too. I never did find a good way without gobbing on tons on makeup unfortunately. Granted a lot of the hairs did grow back, but not nearly as many as were there before. I almost want to think that it was some kind of bruising or something under the skin, but I dunno?
This was back in late October, and just recently I have noticed the 'shadow' starting to be less apparent. But, sorry I have no idea *why* it happens =/ In my case it seems that time has been slowly taking care of it for me luckily. How long has it been since your last session?