Welcome to Android Central! Do you mean that the phone's mobile data internet connection (3G/4G) also goes gray? Does this seem be associated with anything you're doing on the phone, or is it pretty random? Does it persist after a reboot?
Try booting into Safe Mode, which temporarily disables all 3rd party apps. On most Android devices, while powered on, press and hold Power until the Power Off menu appears. Press and hold the Power Off selection until the Safe Mode prompt appears. Tap OK.
If the problem disappears in Safe Mode, then something you installed is causing the problem. You may have to uninstall apps one by one until the problem disappears. If the problem persists in Safe Mode, then it's more likely to be a hardware or firmware problem.