Caramel Coloring

Background: 

Caramel coloring is frequently used in beverages including scotch whisky, tequila, cognac, and rum to darken them for consistency between batches and/or to make the beverages appear older. 

Legal Status:

In the United States, caramel is "generally recognized as safe" [link]. "Caramel may be safely used for coloring foods generally, in amounts consistent with good manufacturing practice (GMP)." [link] 

Gluten: 

Caramel coloring may be derived from malt syrup [link]. Some imported products may contain caramel coloring derived from gluten-containing sources such as malt syrup.  Though highly-processed, some celiacs complain of sensitivity to them. At this point it is not guaranteed that products with caramel coloring are always gluten-free.