I have successfully used Top Flite Lustre Kote "white Primer # TOPR 7527" for that exact purpose. Last winter I had occasion to rebuild the wing on my small J-3 Cub float plane (must be hard water around here ), and I had some dark mismatched material areas that were going to show through the Cub yellow covering. I misted several coats of the Top Flite white primer on the problem areas (not the whole wing) and after covering they were 100% invisible even through yellow covering. I had no problem with the covering, Ultra Cote in this case, sticking in the painted areas.