The red dye is only a marker. The dye that they put into the fuel also contains a chemical constituent that they can detect in the exhaust, so if they have any doubts about fuel color, they can verify if it's on-road or off-road diesel by sniffing the exhaust.
Insofar as probable cause is concerned, the Supreme Court has ruled in numerous cases that your vehicle operated on a public road is not your home - you don't have the same Constitutional protections on a public road that you do in your home.
Most of the "dipping" here in Texas is at farm machinery sales and livestock auction barns where they're checking to ensure that the farmers and ranchers aren't using their off-road fuel in their on-road trucks.
Rusty
Insofar as probable cause is concerned, the Supreme Court has ruled in numerous cases that your vehicle operated on a public road is not your home - you don't have the same Constitutional protections on a public road that you do in your home.
Most of the "dipping" here in Texas is at farm machinery sales and livestock auction barns where they're checking to ensure that the farmers and ranchers aren't using their off-road fuel in their on-road trucks.
Rusty