I thought I'd add this to the day's post, a set of paintings that illustrates the many, many varieties of green used in landscape painting. Green Landscapes a set at Flickr
Here are some tips for mixing fabulous greens:
For natural greens in the landscape use any yellow + blue , but always modify with something from the red family like, transparent red oxide, napthol red, orange, vermillion
Create greens for the distance by adding a blue to the mix, ultramarine blue works well because it has a touch of red in it and it will neutralize the greeen a bit.
High key "spring" greens can be made by using cadmium yellow light, or cadmium yellow lemon, or transparent yellow mixed with phthalo blue, or ultramarine, plus white. Warm them up with a touch of orange, or make very light tints using naples yellow, mellow them out with the addition of some yellow ochre.
Low intensity yellows in many hues can be created by adding black to any yellow, lighten with white or naples yellow.
Very dark green mixes often benefit form the addition of purple.