That is a sharp looking Chevelle. Yellowing of the decals is a bummer, but possibly it's the glue. I know they're already on and it is what it is but in the past I have actually taken old decals and put a few drops of bleach in the water that I release them with, and that helped with yellowing caused by the glue. That's the one thing about a kit that is a light color you risk the chance of yellowing decals. I have a baby blue 66 Mustang that did the same thing