What color green was used during the Korean war?

Vehicles were still painted standard OD Green for Korean war era.

Vehicles were OD Green but paint varied like you said due to fadeing, how well the paint was mixed, the age of the paint job ect, even from lot to lot. Even with modern military equipment, I have seen major differances in shade between vehicles. So pick a shade and go with it, someone would be hard put to prove you wrong.

I'd start dark OD since the M46 was a new vehicle and not an old WW2 tank pressed into service. Although the Korean environment was harsh, the tanks didn't see prolonged combat service since the war ended in a short span of time.

Let me modify the question. What color is olive drab? I have seen a semi gloss dark green through a brownish olive.. Maybe I'm chasing an allusive color. Would Tamiyas olive drab with some black be about right?

There were a lot of variations in the paint, exacerbated by sun and weather conditions. I would think a semi-gloss in that scale wouldn't look just right with the shine, but that's a personal opinion. When I painted my last Sherman, I used a mix of Model Master OD green and faded OD green. It gave it a nice non-uniform look

In a recent article by Steve Zaloga in Military Modelling (UK), he compared the various makers' olive drabs to WW2 era OD. His conclusion was that Tamiya Olive Drab was the most true to the actual hue of American WW2 OD.

However, he cut it down with some Tamiya German Panzer Yellow to add scale effect for 1/35 vehicles.