Sunset Yellow FCF (also known as Orange Yellow S, and FD&C Yellow 6) is a colourant that may be added to foods to induce a colour change. It is denoted by E Number E110, and has the capacity for inducing an allergic reaction.

It is a synthetic coal tar and azo yellow dye useful in fermented foods which must be heat treated. It may be found in orange squash, orange jelly, marzipan, Swiss roll, apricot jam, citrus marmalade, lemon curd, sweets, hot chocolate mix and packet soups, trifle mix, breadcrumbs and cheese sauce mix.

It appears to cause allergic or intolerance reactions, particularly amongst those with an aspirin intolerance. Other reactions can include gastric upset, vomiting, a rash similar to nettle rash and skin swelling.

It is one of the colourants that the Hyperactive Children's Support Group recommends be eliminated from the diet of children.

At high concentrations, Sunset Yellow in solution with water undergoes a phase change from an isotropic liquid to a nematic liquid crystal. This occurs between 0.8 M and 0.9 M at room temperature.