If you saw one it depends where you live, but it could be one of the following:
green tree snake: http://las.new-England.net.au/wp-content/uploads/2007/03/images20070304-035-treeSnake-sml.jpg
http://www.tvwc.org/AssetsGreenTreeSnake.jpg
green tree python: http://www.kingsnake.com/ihs/I.H.S.%202005%20PHOTO%20CONTESTHeat%20pits%20of%20the%20green%20tree%20python%20-%20Michael%20D.%20Kern%20-%20IN%20CAPTIVITY,%20SM.jpg
rough green snake: http://www.wilddelaware.com/wp-contentrough-green-snake-11832.jpg
natal green snake: http://api.ning.com/files/L1ySGyMwLZ3hID057bBHbPN6Eqw8ML160RN4P6rDPxM_NatalGreenSnake.jpg
Asian green snake: http://www.dekayi.info/R_I_P_%20Green%20snake_filestree2.jpg
Hope this helps.
The description you give comes close to a Northern Water Snake. No snake with a green head has a white and brown body but at plain site this snake may look to have this description.
Yellow on top with the body yellow and white mixed,, And
snakes can be all colours except blue and purple
Bright green ! See related link for a picture.
A young common grass snake
An Aussie snake
Green, Orange and Yellow
If the stripes are light in color, maybe even off white it could be a CA king snake.
Depending on the order of the banding - either a king snake or a coral snake.
Only in cases such as: The snake is blue, green, and yellow.
Garder-snake; multi color green, yellow and black stripes length of body.
if it is green it is mean, and when it is blue it only sees you. But when it is yellow it is just a little bit mellow.
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