I think dark green is the way to go, and it is far more likely there was dark green around. But that's not logic, just an assessment of what's likely. But if there was extra dark sea green around, surely any RAF stores master would leave that behind before leaving dark green behind? And if some annoying Yank came along and asked me for green paint, I would give him the stuff I knew I wouldn't be using - extra dark sea green rather than dark green. The military in war-time and in peace is usually very reluctant to part with stuff that might be needed, particularly stuff that senior officers might require to spruce up things before even more senior officers visit. So IF there was a green around that wasn't dark green, wouldn't that be the one left behind or handed out? You wouldn't use limited space on a lorry fir paint you don't need and leave behind paint you will need if you are moving airfield.
And if extra dark sea green was produced but little used, there might be a fair but around?