White diesel is the ultra-low sulphur diesel typically used for road-going vehicles. White diesel also contains a higher concentration of cetane than red diesel. Red diesel is used for certain types of machinery, tractors, and combine harvesters, with a red dye added to differentiate it visually from white diesel.
Red diesel (also known in other countries as gas oil) was traditionally used for domestic heating, though its use has since been replaced with Kerosene (also known as heating oil). Its use is typically commercial, and should not be put into a piece of machinery, plant, or vehicle unless the manufacturer recommends it.