Green is the color associated with the heart energy center.  Generally, the red through yellow part of the spectrum are considered warm colors.  Green starts the cool colors.  When someone mentions green, we usually think of  green leaves, grass and other plants.  Since plants are usually very calm, patient life forms, that gives you some idea of what green does for you.
    In color psychology, green represents tranquility, luck, good health, and nature.  Green is recommended in decorating for it's calming effect.  It also helps relieve stress.  Bedrooms especially should be decorated in primarily blue or green.  I always buy sheets, blankets and comforters that are primarily green or blue.   In television, the room where guests wait before appearing on stage is usually called "the green room" because it is green to help the guests stay relaxed.  Hospital rooms are often painted pale green for the same reason.
     One very interesting study found that green can help slow readers.  When a sheet of green transparent paper was used to cover the book page, students read faster with better comprehension.  Another found that green can improve vision (I couldn't find any details on this one). 

Myths and Legends:

In the middle ages, brides often wore green which symbolized fertility.
Before a fashion show, seamstresses often refuse to mend anything with green thread as it is believed to bring bad luck to the show.
The Legend of Sir Gawain and the Green Knight is a popular tale full of Celtic myth ans symbology.

Healing:

In addition to those uses already mentioned,  since green is associated with the heart chakra, a strong green energy center will help you have a healthy heart and circulation.  Other organs in that part of the body such as the lungs and the liver benefit as well.  If you have health problems in that area, you may need to strengthen your green chakra. 

To strengthen your green energy center:

wear green clothes
eat green vegetables
take a walk in the woods
decorate with green
wear green sunglasses
drink green tea
wear green crystals and jewelry with green gems.  Malachite, peridot and jade are good choices.