Roger,
I believe there were some light blue bottoms on the African corps Spits. They were a totally different color from the UK versions.
The UK Spit colors are Medium sea gray, Dark green and Ocean Gray. Plus Sky for the fuse band and spinner.
Roundel painting.
The way to do that and all your markings is once you put down your mask paint around the edge with the underlying color. Then paint the proper color over it. That way you seal the paint mask first so there is little to no chance of bleed under.