Unless I'm not seeing something everything looks good. As long as there are no Black deposits on the plugs your fine. How many miles are on this engine? If you want, since the head is off, send the injectors off to be cleaned, mr injector is a good place, also have the upper and lower intake manifold cleaned as well as the throttle body. All high mileage engines are going to have dark deposits on the combustion chambers, it is a byproduct of combustion.
I would also get a machinist opinion on the water passages along the exhaust side for piston #4 corrosion due to neglected coolant seem to be wearing it out. Do not forget to reinstall the ground at the back of the head to prevent electrolisis.