Actually very interesting reading the different definitions for the word "Gringo":
In Central America it is mainly used for US citizens.
In Uruguay it is mainly used for English and Russian people.
In Brazil it refers to foreigners from any country.
In Belize I have seen black people being referred to as being gringo, where white people from foreign (non-US) origin didn't qualify for the gringo category.
The word Gringo comes from "green coat" and originated during Mexican-American War of 1846-48, in reference to the American soldiers and the green color of their uniforms. It must have been the Green people then. Guess this Blue guy was innocent this time:
http://abclocal.go.com/kfsn/story?section=news/local&id=5843725