If your barn is like mine, it has white gasoline, white gas mixed with oil, kerosene, naptha, coleman fuel, and diesel in 1,2 and 5 gallon cans. If you do make a mistake and pour 5 gallons of gas into the diesel tractor by mistake, you will be in need of another tractor - you won't be able to shut it down before it tears itself up. The laws are set up to prohibit refilling of cans of the wrong color or marking, but not paid much attention to where you do it yourself. Blue is for Kerosene, Yellow for Diesel, and Red for Gasoline. Certainly makes sense if you can accomidate always having the wrong containers when you need them. The worse problem normally comes when your wife, or brother in law, or someone else is searching for the correct fuel and does not know that the fuel in the can that says DIESEL is really galoline. Then you need another tractor.
Some of us even forget what we put in the can after a few months pass and hope we can smell or feel of the contents and guess correctly. The jugs are really not expensive to help sort out the different fluids, but masking tape falls off pretty quick.