In general, those P-51's in 'bare metal', had the main wing finished in 'silver', a coating made from clear lacquer and aluminium powder, which covered the sealed panel joints and puttied finish.
The fabric-covered control surfaces (except flaps, which were metal skinned) were finished in 'aluminium' dope, with the flaps in bare metal.
However, as the model appears to have a 'uniform' finish, then as suggested, an 'aluminium
paint would suffice for the flaps, and if there is a shade difference between the remained of the airframe, it would not matter much.