I was not sure what red diesel was so looked into it. This is what I found. I would not want to get caught using it or at least state on a public form that I am using it. FYI.........
Red diesel fuel is only slightly different chemically from regular automotive diesel fuel, but there can be a significant difference in cost. The cheaper red diesel fuel could conceivably work in place of the more expensive automotive diesel fuel, but that would defeat the purpose of a fuel tax. In order to ensure that home heating oil, which is minimally taxed, is not used as diesel fuel, which can be heavily taxed, revenue agents require home heating oil to receive a special red dye. This liquid red dye can be detected in even the smallest samples taken for examination.
Using red diesel for reasons other than home heating is generally considered a criminal act, since the buyer did not pay the proper tax for regular diesel fuel. If there is reasonable cause to inspect a vehicle's fuel tank or storage tank, inspectors can quickly and conclusively identify the presence of red diesel and take appropriate action against the offender. Without the creation of red diesel, it would take a trained chemist to differentiate between home heating oil and automotive diesel fuel.