Wow, no one's mentioned the four humours yet (based on searching for 'humo' on each page, I'm not reading 4 pages of comments... These are very similar to the classical humours that the Greeks thought ruled health and personalities: blood, phlegm, yellow bile and black bile, from which we get the adjectives sanguine, phlegmatic, choleric and melancholic. It's mostly rubbish but it does turn up in fiction quite a lot, here's some examples:
Gold - Yellow bile - Choleric - Extroverted/Task orientated - Slytherin - Leonardo - Sheldon Cooper - Arnold Rimmer
Blue - Phlegm - Phlegmatic - Introverted/People orientated - Hufflepuff - Raphael - Leonard Hofstadter - Dave Lister
Orange - Blood - Sanguine - Extroverted/People orientated - Gryffindor - Michaelangelo - Howard Wolowitz - Cat
Green - Black bile - Melancholic - Introverted/Task orientated - Ravenclaw - Donatello - Raj Koothrappali - Kryten/Holly
See also http://tvtropes.org/pmwiki/pmwiki.php/Main/FourTemperamentEnsemble
and http://www.youtube.com/watch?v=dtsmluPK7Ug (although the latter gets it a bit wrong).
And due to the fact that I both know and care about these things you might be able to guess it's not easy being green...