The problem is with using on road in off road motors .
There is now no difference in on-road and off-road diesel, except for the red dye. In the past, off road diesel had a higher sulfur content. However, some time back the govt. put a stop to the use of high sulfur diesel. So, now they are the same, except for the red dye indicating that no highway tax has been paid on the off road stuff.
I don't know what the rules and content of your fuel in your states are but here we call it Purple fuel and the only difference is that it is coloured. It comes from the same source as regular fuel. Farmers are only allowed to use that fuel here as certain taxes have been taken off the cost. If you get caught on the road or using it in construction machines for non-agriculture reasons you face high fines and an audit from the tax department.
Farmers are not the only ones that use it. We also use it here in all mine trucks and other machines eg graders as they do not go on any public roads ergo why pay the road tax portion of the perlitre cost, which is considerable