Annatto is used both as a spice and as a natural food coloring. It is gluten free according to the list of “safe foods” published by Celiac.com. It is OK’d by the Celiac Sprue Association in the 12th edition of its Gluten Free Products List.
Annatto is important to us primarily because it is one of those “mystery words” that cause confusion when we are attempting to wade through an ingredients list. Like all food colorings, it can cause reactions particularly in children. Here’s a link to a worksheet published by the Food Intolerance Network that addresses that situation.