Unless you're using dry transfers apply a gloss coat BEFORE you
decal. If you don't, they will silver no matter how much setting
solution you use, and the carrier film will be extremely obvious.
You might try this; gloss coat, decal, then gloss again. Follow
with a FOG (I.E. VERY light) overspray of the original color. This will
tone down the lettering and restore the look you want. When you think
that just a little more will do it STOP!!! Works for me. This is one
place where "Less is more" is valid advice.