Caramel coloring *can* be made by heating wheat or barley malt. All caramel coloring is made by heating something that contains sugars until the sugars change to caramel. There is some sugar in wheat, so it is certainly a theoretical possibility to make caramel coloring from wheat, or barley. It also meets the legal definition of caramel coloring set by the USDA in the United States to use materials that originated from barley or wheat.
The magazine Gluten Free Living has stated that they consider caramel coloring to be gluten free.
I know that I react in a predictable and recognizable way when I accidentally ingest gluten.
I ignore caramel coloring when I see it listed as an ingredient. I consider it to be such a very low risk for containing gluten that I would suffer more harm by avoiding foods with caramel coloring than by possibly being exposed to it if I did ever encounter a food with gluten-bearing caramel coloring.
The legal definition of Caramel Coloring from the USDA does allow it to be made from barley malt, so it is possible that caramel coloring could contain gluten. In the U.S.A. caramel color must conform with the FDA standard of identity from 21CFR CH.1. This statute says: "the color additive caramel is the dark-brown liquid or solid material resulting from the carefully controlled heat treatment of the following food-grade carbohydrates: Dextrose (corn sugar), Invert sugar, Lactose (milk sugar), Malt syrup (usually from barley malt), Molasses (from cane), Starch Hydrolysates and fractions thereof (can include wheat), Sucrose (cane or beet)." Also, acids, alkalis and salts are listed as additives which may be employed to assist the caramelization process.
The question in my mind is how much of the offending protein structures are going to survive this heating process if barley malt is the source. And then secondarily how much caramel coloring is going to be in a food.
If 1/100 of 1% of the caramel coloring contains gluten, and caramel coloring is 1% of a food substance, it is pretty darn diluted, if it is there at all.
The leading manufacturers of cola sodas in the USA, Pepsi and Coca Cola, both say that the caramel coloring they use is gluten free.
I hope this gives you the information you need to make a decision that fits your needs.