I can confirm that my father referred to ROP and it's origins, per Danny's post.
An Aussie Merchant seaman was adopted by the parents, he worked tankers and said they would walk along the deck tipping powder -dye into the various tanks before unloading....the main ones I remember, Regent Green, Aladdin pink, and of course, the famous Esso Blue.
In the late 1960's I lived at Leigh on Sea on the Thames Estuary. there were lots of boats with Morris Vedette Petrol-Paraffin engines (basically a 1500cc converted car engine) start on petrol, warm-up, then switch to parafffin .
Petrol 4/6 a gallon,(22 1/2P) paraffin 1/10 a gallon (~8p) Prices seemed very stable, back then, other than the chancellor's annual hike on beer, spirits and fags (only posh people drank wine! I was about 17 before I tasted any!)
in the 80's I ran a village garage/filling station I sold paraffin, there were 2 grades- "premium" which I could dye with a powder left by my predecessor (a tablespoon to 300 gallons! lovely deep blue!) and 28 second burning oil....which is "impure" paraffin, -light heating- oil....the heavier ,35 sec oil is also known as gas-oil or "red" or , in it's clear form, Road diesel.
"Slab" Murphy had a farm straddling the border between Northern Ireland and the Republic tankers of "red" would drive in from the North, tankers of "white" came out through the Republic, to find it's way on the ferry and the UK market.
Murphy is purported to have supported the IRA and boasted thet whatever bright chemist the Customs employed to mark "Red diesel" he would pay more to a brighter bod who could remove all the C&E markers. Red is less than half the price of road-fuel!
Apologies for thread-drift, hope it contributes something.