Thank you 16.
I really had to fight this one. As an experiment, I made a green from Indian yellow and French Ultra Marine Blue. Almost black and then painted the paper panel like William Alexander did with a more liquid white. When I went to overlay the sky I realized the trails of my knife were more blackish than I wanted so I really had to lighten the weight on the knife. As a good part of the deal, the trees painted directly into the mix with a yellow really worked wonders. The reds went in equally as well. Next time I try such a stunt I be sure to test my grey before I cover the panel.