Are you sure there wasn't a sign? I know I saw a gas station in MT that advertised regular diesel, and red diesel. Price was much lower, so I was tempted, but decided to drive on by...

I have been told that the 'offroad' diesel has added sulfur in addition to the red dye. Supposed to make it easier for a cop to 'sniff you out' (hehehe) if you are trying to cheat.
Of course, that also adds to air pollution, so farmers are inadvertently adding to acid rain, but it can make older diesels happeer because they were designed when fuel has more sulfur than today.

I would be concerned about possible legal problems if you get checked. Probably low odds being a car, but...
Ask the station manager, and try to take some extra trips in the coming weeks. Try to run the tank pretty low to dilute everything as much as possible when you get your next fillup which will hopefully be with legal stuf.

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1971 220D/4-speed ~250K mi. Family owned (dads side) through three generations since <5K miles.
1992 Chrysler LeBaron, 3.0V6 125K. Family owned (moms side) through three generations since new.
1977 Chevy Camaro Continual hotrod project
1970 Cadillac Sedan DeVille 472ci and nearly 19' long
1974 Fiat Spider Still needs work