The real aircraft were mottled with a spray gun, so airbrush is the best way to replicate it on a model.
I've seen factory photos of 109s on the assembly line, and they seem to be painted with the RLM76 blue underside color all over, as a primer, first. Then the topside colors are applied next. That's also the way i paint my 109 models.
http://www.inpayne.com/models/models_me109.html