James Gurney paints cinnamon ferns in gouache. His sketchbook page is primed with a yellowgreen underpainting that simulates the typical backlit leaf color.
Gumroad tutorial: "Gouache in the Wild": https://gumroad.com/l/gouache
"Casein Painting in the Wild": https://gumroad.com/l/casein
"How to Make a Sketch Easel": https://gumroad.com/l/sketcheasel
Gurney's videos also available as DVDs: https://jamesgurney.com/collections/v...