Originally Posted by eagleskinner
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.
Not sure about UK but in US fuel has always been dyed to identify octane rating. Seems like the purple was 115/145 octane