Almost every refinery in the country has converted their sulfur fuel to ULSD. Even the construction equipment and farm tractors this year have DPF and SCR. So even the off road folks need the ULSD in their machines. So the fuel is the same, just dyed Red to show that no taxes have been paid.
Be aware, that it takes a LOT of fuel thru your system to get the red color out of your fuel. It will also stain your fuel filters. So the cops, if they are checking in your area, really don't have to work very hard to determine if you were running it. Fines can be as high as $10,000.
Around here, they seem to check folks that have aux tanks in the back of their trucks. The kind of tank that you would use to haul fuel to your back hoe. I guess they figure you have more of chance of topping off your own truck while filling up the back hoe. On rare occasions they will set up check points at Fairgrounds/Rodeos where lots of farmers/ranchers have their trucks, I guess they believe those folks all have yard tanks to fill tractors and would be tempted to fill their trucks from those same tanks.
The avg guy driving the hiway with no aux tank probably will not get checked unless somebody sees you at the pump filling with the wrong fuel.