Sudan III is a lysochrome diazo dye. It is structurally related to azobenzene.
Sudan III
Fuel dyes are dyes added to fuels, as in some countries it is required by law to dye a low-tax fuel to deter its use in applications intended for higher-taxed ones. Untaxed fuels are referred to as "dyed", while taxed ones are called "clear" or "white".
Plastic jerrycan containing 'red' diesel.
Fuel pumps in Ireland, with green gas oil and red kerosene, and notices that it is an offence to use marked fuels in a motor vehicle.
Petrol station in England, with 'red diesel' available for a lower price, but only for "off road use", i.e. agricultural machinery and similar.
Diesel (black) and dyed fuel oil (MPÖ; red) dispensers at a St1 petrol station in Tornio, Finland.