The airbrush with its capacity for transparency will allow you to lay a film of color on a wash and subtly or radically alter it. When I was in college I was told that you could make shadows by adding complimentary colors. Experience taught me that it was the fastest route to brown. However the layering of a transparent on a wash coupled with the fact that you don't have to wait till it dries to see the result will let you put a thin glaze of violet on field of yellow. Now imagine what would happen if you took a series of sympathetic colors and layered in such a way that you could get a rainbow.
Time means nothing to an airbrush.
Of course time means nothing to my brother either. In the case of the airbrush you are not constrained by the time that is dictated by the wash. Do a wash now, finish it in a week or so. In that odd world called unintended consequences, there is the fallout from the airbrush. One is that the airbrush is stingy with the use of water.