As a painter, most of the technical details are lost on me, though I get the gist.

Looking at the results, it seems that the author defines a base color (green for the leaves) and moves up and down in brightness using what amounts to a multiplication for the shadows and an add for the lights. The result feels a bit harsh and unnatural.

I would suggest that he also plays a bit with the hue values.

1. That he darkens the lights but moves the green towards yellow.

2. That he lightens the darks, but moves the green towards blue.