Green as the color of hope is connected with the color of springtime; hope represents the faith that things will improve after a period of difficulty, like the renewal of flowers and plants after the winter season. In the stock market, green indicates the stock is trading higher than the previous day's close. 
That's why you can usually see investors wearing smiles when green stuff shows up. 
Okay, let's see some green stuff, and the happiness came along.
@Kit Kat Crazy: send it ...