Sounds like someone has been messing with the settings. Was this either a used camera or a "floor model" demo that could have had the settings changed? Check your manual for the method for resetting the settings to default.
Auto focus on a blank sky is problematic; there's nothing to focus on (stars might not be good enough for the autofocus to work properly). For night sky shots, I would use manual focus and set it for infinity.
Within the last week, I read about some kind of setting adjustment that can change the overall color hue of a picture (but that may be only black an white pix - I don't remember). Or perhaps the White Balance adjustment is off. Do you shoot raw (NEF file extensions). If you do, you might be able to correct that in the computer using the white balance.
Is the 18-70 the only lens you have? (I thought the "standard" kit lens was the 18-55). I had been using an 18-200 lens and found out later that the lens had focus problems. When I went back to the 18-55 kit lens, I got sharp pix. If you have another lens, check the focus using that lens. Do a search for the "Where is the Focus" thread. I received some good advice there about my focusing problems.