Two years ago, I had an IRS agent come to one of my stores checking for dyed fuel in road vehicles. Never had that happen before. I use clear fuel although I do have dyed fuel tanks for off road. I recall seeing a sticker on a gas station pump that said "due to current diesel fuel shortages, some fuel may be dyed". If you use undyed fuel as well as gasoline, for off road, you can recoup the tax on you tax return. That requires a lot of record keeping so I just let it go.