this is mostly regarding British factory-applied colour post-WWII but I'm a bit confused about the information I found online.
The way I understand it, British post-war vehicles were still painted SCC 15 Olive Drab until ~1955 (see Dick Taylor: http://network54.com/Forum/47209/thread/1378716606).
But then there is Clive Elliott's research (British Army Green Paints: http://www.warwheels.net/generalinfoindex.html) that suggests that vehicles were painted BSC 24 (later 224) Deep Bronze Green starting in 1948.
So am I right to assume that new vehicles were painted DBG in the factory but repainted SCC 15 by the crews?
Or is DBG just a "recommendation" and vehicles left the factory in SCC 15 until DBG became the main colour in ~1955?
While I have no idea if vehicles in service (as opposed to newly procured) were repainted; the British brigades deployed to Korea from the UK were ordered to repaint their vehicles in SCC15 for the same reason it was done in WW2--uniformity with their US allies and simplification of logistics. That the order was necessary says that DBG was already in common use in 1950. Later Korean war photos seem to demonstrate that this directive was either rescinded or abandoned as the war went on. I cannot address the British army outside of the Korea context with any authority but I suggest that DBG was introduced gradually, probably via new procurement. The UK was nearly broken by WW2 and repainting an army a slightly different variant of green would be an expensive luxury for a nation still on wartime rationing.
If you're modeling Korea, go with SCC15 unless your photo indicates otherwise. For the army worldwide, others here can address your question in more detail with better documentation.