Before the war the Enfield rifles were inspected four times a year, three visual inspections and one complete tear down inspection. When the the Enfield was assembled the barrel channel and receiver area was packed with mineral jelly (Vasoline) to protect the metal parts under the wood line from corrosion. After Dunkirk ALL rifles had the mineral jelly removed and were painted with a green primer, and the troops were issued raw linseed oil to oil the stocks once per month. After the war the use of mineral jelly was resumed until the rifles were painted with suncorite black paint.
If the rifles were put in storage after the war and then sold off as surplus they would have green primer on them. If the rifles were kept in use and issued the green paint was removed and mineral jelly used until painted with suncorite paint. I have a South African marked 1950 Mk.2 and the mineral jelly had been removed and the barrel and receiver were painted with a semi-gloss black enamel that started to come off when cleaning the rifle with odorless mineral spirits.
So the green paint is part of its collectible history, if you are not a collector and plan to use it as your shooter then remove the green primer and repaint with high temp barbeque black and oil the stock with RAW linseed oil.