The Grape scheme was one of the earlier aggressors schemes and pre-dated the 1980 letter specifying most of the later camouflages (See the F-5E aggressor color scheme history section). As the grape scheme pre-dated any official specification there was some artistic license taken in its application and therefore there is a need for decent references of the particular aircraft you are modelling.
Most aircraft in the Grape scheme had black radomes (I've never seen otherwise) and also featured the standard unpainted areas of the rear fuselage common to all F-5Es.
