A rainy day during a plein air workshop on Long Island several years ago became a day of studying green paint. The instructor said, "Make as many greens as you can with colors you have". I produced the green chart (pictured below) with the color mixtures listed below each test strip.
Then I cut out the center of each strip. If you hold it up to the green trees or fabrics or nature object, you can see what colors to use in creating the color.
I also have a palette of those colors to make the greens. This way the greens do not mix in with other colors on my separate warm and cool palettes.
The only green watercolor I buy is Winsor Green. I use it for the green is stop lights. One tube lasts forever.