Environmental crusader Cameron Diaz is hoping to turn the next Shrek movie all green - by asking producers to consider a film with an eco-friendly message. The actress, who plays ogre Princess Fiona in the Shrek films, has started campaigning to make the fourth film all about the environment. She says, "That's something I've been on Jeffrey's (producer Katzenberg) ear about, that the swamp possibly could be in danger." And Diaz has the backing of her animated mother in the Shrek films, Julie Andrews. The Mary Poppins star says, "What better way to get a message across than with something that's so funny?"