"The most interesting passages.. " - the gradated mask technique

I need to record how I did this before I forget.

I've been experiencing somewhat of a breakthrough doodling around on the ground and trees, and this is a new technique I invented for it:

Painting on a new layer (the light clods in the dirt ridge behind Fafhrd). I used a light cream color, the lightest color in the dirt highlights, but I painted the entire clods all as individual shapes just using that one color. Then I used the magic wand to select the transparent area on that layer and did an Inverse, so now I have the highlights I just painted selected. Make a Hue/Sat adjustment layer, and click the box to use the selected are as a mask (that's not the exact wording). Then I was able to adjust the hue, saturation, and lightness of those selected daubs of paint.

But here's the new part - I then painted onto the transparent parts of the mask using various values of grey, to make a gradated mask. So that when I finally merged it down onto the background copy each brushstroke now goes through a transition of all 3 elements of color - value, hue and chroma.

My own somewhat mangled quote of Richard Schmid - "A paint passage is more interesting if it includes a shift in color or value. The most interesting passages include both".