Gringo was a name given by the Mexicans during the Mexican-US War.

Green GO!

because US troops were wearing green uniform, well so I have being told.

In the Dominican Republic, a Gringo is a person who's Nationality is Mainly U.S. American, but Canadians my be called Gringos too, white chicken are called Pollos Gringos (gringo hens), anyone with Blond Hair and green or blue eyes and pale skin is a gringo, including many white dominicans.

This is not a derogative name, is just how Dominicans reffer to Americans or Canadians since Canadians and Americans often share the same customs and languaje.