Way back when...
The English army dyed Avgas with a purple dye to prevent us 'orrible tech types and other ground handlers filling our cars with it. If you were ever caught driving through camp gates with a purple exhaust, you were very soon making acquaintance with the monkeys.
Funny thing is, the only person I knew who got caught was a peelow.
I wonder if they still do?
(P.S. I know you were talking kero, I wonder if it could be dyed for a similar reason)