I was using GPS navigation and depending upon the hour, the screen will turn to a dark gray color. I assume its so you don't have a ton of bright light coming from your phone as your drive at night. The Navigation app went from light to dark at a specific time. I think it happens based on sunset for a specific time zone. I have seen it happen twice now. Someone put a lot of thinking into the app. I wanted to hit up a Walmart. Typed in Walmart as I was driving to grandma house and bam, the Navigation app listed all the Walmart's along my route. Google/Android puts a lot of love into their apps. Also, I didn't know you could put your phone to sleep and the Navigation app will still call out every turn with the phone in sleep mode. I always monitor my battery temperature as I drive and leave the AC blowing a little on the phone to keep it cool because I thought you always had to leave the screen on. And I would unplug my car charger if the temperature got to 108 on my phone. Well, I don't have to do that anymore. I can leave the phone plugged in, put the phone to sleep, and the battery temperature will stay low. But I still get my turn by turn directions. WOW!!!