Howdy,
Diesel Fuel= comes in many forms
All comments are by today's current standards
Road Diesel= clear, sometimes a greenish tint. 40 or better cetane. known as road tax applied. currently known as ULSD 15ppm or less
Older diesel was LSD 500ppm or less
Off road diesel= ULSD 15ppm or less, no road taxes paid. dyed red
some still might find some LSD 500ppm being sold. it should all be gone by now. Yes, some industries call for it (Locomotives)
Home Heating Fuel= usually does not have the added lubricty additives etc. Dyed RED, but is taxed. TAX is because of use. NOT road tax, but your usual tax. Because the price of Off-road diesel could go under the price of Heating Fuel, a bulk delivery could put off-road diesel in your house heating tank. Dyed red, but taxes are paid due to its use. I have scene a delivery truck fill a farm tank (off-road diesel) and a home heating tank out of the same section from the tanker. Farm use NO-TAX, and the Home heating fuel TAXED. A normal delivery of heating fuel could be diesel #1, also might not have any fungicide additives also.
Red Dye= is in the fuel to show no road taxes paid. If the DOT straws your tank (Regular pickup etc) and pulls any red color out, you are in big trouble. Your messing with the IRS and taxes.
so, in summary
road taxes paid, clear diesel
taxes paid, heating use, dyed red
no taxes paid, farm use (off-road) dyed red