Why does the government restrict dyed fuel to off road use?

[97idi]

here in md (near the jimmi cone in mt airy) their is a station that sells generic fuels both diesel, kerosene and gasoline, the pumps have too be advertized for 500ppm of sulfer content because they switch between 15 and 500ppm also the kerosene is undyed and i to notice a difference when i run offroad in my truck that is dyed