That is going to be a hard one. I did this once. I cleaned up the existing paint and then took it do a paint shop to have the old paint matched. Applied it and polished both old a new and it did just fine. You could still see the diff if you looked closely. Now with that in mind I had no decals or painted decoration to work with. BTW I used and airbrush to blend the paint. Now keep in mind I am a woodworker not a guy who paints metal or cars. I would get some advice from an auto painter they know how to do great things on cars to blend paint and not see the patch. Good luck with this painting repair