Many thoughts here, resulting in “pick which one you like best.” It’s got to please you, the maker.
1. In nature, trees and grass are never just one shade of green. There’s a mix of forest green, blue-green, yellow green, grey-green. So feel free to be artistic by imitating nature. Mix up shades within each tree.
2. Keep all triangles within one tree the same, but vary the trees.
3. Think of sunlight hitting one side of the trees. Put all lighter greens on one side, all darkers on the other .