Just as a matter of interest, the standard factory scheme for the PA-18's were not all over yellow like on the J-3's.
Most would have a two tone with a white or off-white as a base colour.
This colour is matched to the original yellow of the J-3's. It is called Lockhaven Yellow from Stits. Not sure what a model paint for it would be.
I do realize judging colour from a computer screen is difficult.
Theuns