
(and no one posts pictures of the size of the brush to use, or what RGB values constitute an area that is too bright and needs to be darkened and vice versa)
No pictures, but a video
At lynda.com, there's a series of Videos by Chris Orwig.
You can watch the first few as a trial. In the "Enhancing the tone of the lips" and "Adding dimension to the face" he uses (a variation of) this technique.
He uses Soft Light instead of Overlay. Less strong effect, same basics. Also, he sometimes paints with color instead of B/W.
Link
Watch as much as you can, then maybe sign up