Trees, as in most objects, should have at least three values to make them three dimensional. They are never just green or just any one colour. They are of many colours. Various shades of green, red, burnt umber, orange, blue and purple are some of the colours that go together to make trees. I'm not talking Autumn either. These are summer and sometimes winter trees.
Take a close look at some well known artists' cards and you will see many colours in trees. You can't get the right effect unless you use lots of colours. I buy artists' cards from time to time just to study their art. You would be surprised what you can learn. A word of caution though. Never copy another artist's work.
It's best to learn from many artists and not just one. This way you will keep what you need and discard the rest. You will develop your own style in time and you will have a broad knowledge of painting in general. If you continue learning from only one artist you will eventually paint like that artist and your style won't be your own.
