What is happening is that the decal is "silvering". It is not setting on the paint snugly and the light is getting between the decal and the paint. If the decal is dry, setting solution may not help.
I build race cars for the most part, and therefore, have to deal with a lot of decals. I strongly recommend that you cut as much of the clear decal from the actual art work as you can. It minimizes the silvering effect.