Don't know where you go that from, Chris, I'm much more into German stuff: half of my family comes from there! France still has a boatload of colonies left; springing to mind are French Guiana like you said, Martinique, Guadeloupe, and then French Polynesia and a ton of little islands dotted around. These tend to be split into departments as in France, so therefore use the currency. I'm certain for the first three that they use the Euro, not sure about the rest.