Treen

The Treens were a species of green-skinned humanoids led by the Mekon. In 1991, Dan Dare and Digby of Earth visited a Treen colony where they made an appeal to donate money to charity. The Mekon initially refused along with several other aliens, but was convinced with the assistance of the first seven incarnations of the Doctor. (COMIC: The Totally Stonking, Surprisingly Educational And Utterly Mindboggling Comic Relief Comic)