Can you be a little more specific with what your trying to do Raul?
Depends on who's decal paper your using and what color Krylon. However; in all cases it has to be done in very light misting coats until you build up the overall color your looking for.
As Phred mentioned spary just a little to heavily and it'll wrinkle the page in a heartbeat.
Personally I've done this with Old formula Krylon White, Yellow, a couple Blues and Red. Black for some reason ALWAYS wrinkles the paper regardless of the paper brand or how lightly it's misted.
From some time now I've switched to Only using Decal papers from Micro-Mark. A little more expensive but always exactly what I expect and every single sheet is perfect.