Robh Ruppel doesn't this almost effortlessly. Though I am not sure how he quite does it . I have been doing some paintings to explore how he might go about it , this is one of them.
Still much to experiment before I can really have a solid idea of how I will go about achieving that look
I hope I can help but I went to Robh's workshop at CDA a few weeks ago. If I'm understanding what you're getting at, I believe he just uses a simple brush (he doesn't have a ton of brushes) and just messes around the brushes settings and then the hue/saturation stuff.
This is a technique that I would like to learn as well.