Being as your airbrushing, you might want to try a bit of shading with it, mix up a lighter blue, and spray it from above only (or wherever the light comes from).
then go about your usual washing, edge highlights, other colours as usual
This is what I do with my purple space marines, spray the primer, purple basecoat, a mid purple from a 45 degree downwards angle all around, then a lighter purple again from directly above, then a wash and an edge highlight before doing the secondary colours.