What are these 4 spots on the wings and fuselage of the A-10? I can't seem to find a closer shot of their wings but each spot looks like a small target with a dot and an outer circle, mostly in red, but some are in black.
I am fairly sure that these are the fuel hatches. They are placed right over the wing and main fuselage fuel tanks. (The hatches are where the fuel is put into the craft, not drawn out for sampling). During ground fueling, the hatches are used to refill the tanks.
Nicholas got the geist of this one. The red circles are marking on the four gravity fill fuel tank ports. The A-10 also uses a pressure fueling port is located on the port landing gear fairing behind an enclosure for most refueling since it is easier and faster.