Hi Archer. Turn it down to 0% (which is still something). Also, make sure AutoFlow is switched off. If you're using the mouse, you can then do single-clicks to add as much or as little spray as you like to add to small areas, or do long strokes that wont build up too quickly.
As an alternative to just using white for lightening, you could use a ligher version of the colour you're lightening.
Which version of ArtRage are you using, by the way? I stepped the flow of the airbrush back a bit in 2.11
Yes, you can do highlights and shading on a separate layer, with partial transparency. Unfortunately the transparency is lost if you merge the layers, but it does remain if you're exporting the result.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"