The green pipe is a special pipe found in World of Goo. Like its red counterpart, the green pipe only accepts the one-of-a-kind Bright Green Goo. This pipe and the goo it collects are only found in the level Alice and Bob and the Third Party. Other green-colored pipes in Chapter 4, like in Hello, World behave identical to the normal pipe.
The green pipe is considered an oddity, as it only appears once, only collects Goo that appears just once, and has look-alikes that do not behave identically to it. It is most likely just a red pipe with a different graphic to suit the new chapter, as the Bright Green Goo is most likely a cosmetically altered version of Small Beauty Goo.