Is this the Tammy Tiger in the build thread from of few weeks back, in Tamiya Dunkelgelb?

If so, you may not want to hear this, but that paint is so dead flat, you need to gloss coat it before decals. If not the whole tank, at least under the decals to prevent silvering. It's just the way it is. All waterslide decals have a sealing coat on them that tends to be glossy, you'll just need to overspray flat after they are down. The normal modeling/decal procedure is: prime, paint, gloss coat (Future is the best), decals (with solutions), gloss again to seal, washes, filters and then a flat coat or dry pigments will will take off the shine. That is done on tanks, planes, whatever and will give you the painted on look.

There's a few good sets out there. Archer makes 1/16 dry transfers too (still need gloss coat and seal).

Good luck on the job search.