I want to add color and intensify the value contrast at the same time. Layering tool in Artrage is a wonderful tool to do that. You can try out different colors to achieve what you want before you actually merge the layer with the under paint. The combination of layering and the use of airbrush tool allowed me to do a more detailed work than I would normally do with oil paint. Wonder what I would do when I go back to do oil paint.
Continue having fun learning new tricks. Next is to learn how to do cut and paste.