I know of one fisherman who was caught with red dye in his then new Cummins Dodge. That would have been around '93 or so. Ended up with somewhere around $20k in fines by the time the investigation was done.
The suspicion was one of the other fishermen ratted him out. They're pretty cutthroat and hold grudges.
My father-in-law had a logging operation. He had a large storage tank for dyed diesel. It only went into skidders/porters.
His own pickup was gas. He said it just wasn't worth the risk. Fines added up pretty quickly if you were caught.
That one instance was the only one I knew of. The FIL's take on the situation seemed to corroborate that, at least locally, it was taken pretty seriously.