What is "sunset yellow fcf"

Sunset Yellow FCF (also known as Orange Yellow S, or C.I. 15985) is a petroleum-derived orange azo dye with a pH dependent maximum absorption at about 480 nm at pH 1 and 443 nm at pH 13 with a shoulder at 500 nm. When added to foods sold in the US it is known as FD&C Yellow 6; when sold in Europe, it is denoted by E Number E110.