Could you give us a little bit more information? Does your penis hurt when this happens? What do you think it is? Have you gotten any cuts? Did you masturbate and this happen or did you just get erect and then it starts happening? How much is it?
What kind of green is it? Is it the left or right side of this smiley:
Or bright like this one:
or even lighter and clear, like precum mixed with it.
Do you eat anything that might cause this? Please tell us.