Torqu pro and code P0307 misfire cyl 7

As some of you know from my previous posts I am having a taping noise on the right side of the engine when it starts but almost goes away when warmed up, I am taking it to my mechanic Monday to leave over night, on top of this my gas mileage just went from 7.5-8 miles to a gallon to 6.... (no leaks of anykind found)

I bought the Torque OBDII reader and this morning before I hooked it up I started my truck and it stumbled...but what really concerns me is I thought the exhaust had a blue tint from a cold start (hoping it was just trick of morning light) after hooking it up it gave me one fault ,P0307, I looked at all the connections hoping to find a loose connection or broken wire, no such luck.
Should my oil pressure indicator sit dead center or a little below dead center?