They can be painted either the FS36081 that Stik mentioned, or they can be painted to match the adjacent camouflage pattern. Same goes for the flap coves on European 1 aircraft.
That info comes from Fairchild drawing 160D900006, December 1978.
Edit: Is your Academy 1/48 A-10 an A-10A or A-10C? If it's Academy's new A-10C, I don't think there have been any A-10Cs painted in European 1 camo.