Depending on how dark you want the veichles you could also undercoat thhem black and then spray blue. If you are a bit carefull and don't spray too heavy a layer of blueyou will get as minor shading effect.
Alternatively spray everything white and give it a coat of thinned down dark blue (Regal or Midnight blue) which should leave the edges with a bit of highlight. Optionally you could coat everything with ultramarine blue before the wash.
The way I paint my ultramarines are first a coat of regal blue (white spray primer for metal units) then drybrush from ultramarine to lightning blue. sometimes I also give a quick wash of my old Regal blue (waaaay old pots) which has a slightly less "blue" shade than the current colour.
Then it is a simple matter of adding detail to suit your taste.
I hope thhis helps.
Cheers!
