Strange color on AFT Gecko

Question
Hello, and thank you for taking my question! I have a 2.5 year old african fat tailed gecko, a female, named Marv. And I've hd her for four weeks, all the while she's been doing fine, eating 4-6 crickets about three times a week. Usually, she is agressive about those crickets and gobbles them right up. Yesterday, I placed four large crickets in her cage, and it took her over twenty-four hours to eat three of them. Four days ago, when i put five in her cage, she took about three days to eat all five. Another thing: normally, she is a nice brown, dark brown color, vibrant for being brown. Well, yesterday, she was brown and grayish! Very strange for her, I thought she might be close to shedding, but not so. Today, she is back to her normal brown colors. Summers here in PA aren't predictable, and while I've had a house lamp over her cage, it worked for several weeks, but the last five days, the day high temp has been around 84 degrees and mid 70s at night. I now have placed a heating pad beneath the cage in addition to the lamp.

I'm still new to this, this is my first gecko --- so please correct any mistakes I'm making, and I'm open to doing anything I can to keep Marv a happy little reptile!

Answer
Hello Jenn,
Are you leaving the crickets in with her all of the time?  If so, that can really stress her & they could also bite her.  
What type of lighting are you using, just a basking light in conjunction to the undertank heater?  is it a bright white light?
If she does not eat the crickets in a few hours, I would take them out.  
What do you measure her temps with?  
Everything sounds pretty good setup wise.  What type of substrate are you using?  
Do you use calcium supplementation?

Tracie