Like Woods stated,Diesel fuel will burn blue,or in heavy concentrations,black. Gasoline burns black if fuel mixture is too rich.Un-burned Diesel white smoke? Transmission fluid burns white. I had a stuck vacuum modulator,in a '65 G.M.C.,and you'd think I was fogging for mosquitos!! Cleaned the valves and top cylinders,though Coolant will cause "white smoke",but actually it's steam,not smoke.
