No worries.
The rear cowling does have a faint line in it where the blue/white transition is. You will be able to see it if you havent already primed it. I went with the photocopying the decals route and its okay, although I might be tempted to mask the bare plastic, prime and paint the white bit, then prime and paint the blue bit. SOunds wrong but I think it will work, and it will gve you a very precise tranisition. I'm considering this for painting the multicoloured B188.
I just remembered another annoying thing, the Allianz and BMW Power decals that are part monocoque and part rear cowl. You have to put the rear cowl on to line them up, but the carrier film crosses the gap and so any movement to the rear cowl fouls up the decals. Make sure you dont move the rear cowl and be patient... when dry use a sharp knife to separate them.
All the best,
Bill