The off road diesel has the red dye in it to distinguish it from on road diesel. The off road, or ag diesel, is the same except for that red dye, and of course the 70 cents a gallon cheaper it is than the on road diesel.
Now, as someone has said, the Law usually hit a sale barn and test the P/U truck tanks while a sale is going on. That red dye does NOT come out of your tank as soon as that tank full of off road diesel is used up and it can take months before it clears out. In the meantime, you'd test positive for using off road diesel in your on road vehicle, which equates to a $10,000.00 fine when caught with red dye in your tank.
Of course, with the on road diesel prices today, $10,000.00 isn't really that much, if you get to use a lot of off road diesel before you're caught!! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
Seriously, it's bad business to try and use any off road diesel in your on road vehicle...IF you get caught!
Living in Texas, I have the permit from the Comptroller's Office to buy off road diesel. A lot of places here won't sell it to you now without that permit.