I believe the J-20 construction built RAM into the construction material for their aircraft. They are more like panels shown in some of these pictures after your post than actual paint. Although they may also apply paint based stealth coating for further reduction.Radar absorption material are very similiar use by early production of f22,big problem when flying supersonic the RAM can easily torn away away.according to usaf,after each flight ,it needed something 14 hours to check any "leak"