Our trek through landscapes that inspired Canada's Tom Thomson and The Group of Seven

 I use transparent watercolours for a purpose. They are transparent.

Look what happens when I apply YELLOW paint (Quinacridone Gold) over the left-hand side of four, dry strips of red. They turn orange. Look what happens when I apply BLUE paint (French Ultramarine Blue) over similar dry four strips of red. They turn purple.

Similar changes in colour would be seen by applying YELLOW over BLUE to make green.

Since grass and trees are green I wanted to see what would happen if I painted a scene in yellow (of different intensities), let it dry, then apply blue over the yellow. The result of this test is shown below. I mixed no green in this painting, not on my palette and not on the watercolour paper. Green appears because I glazed transparent blue over a dry yellow base. Neat.