It might help if you specified which one, as there is Angel Green and Goblin Green
These were primed with Army Painter Angel Green, which is quite close to Caliban Green (Goblin Green is lighter):
If you have 450 models to paint, buy an airbrush, and prime with Vallejo Nato Green (buy the giant size one), and then give it a coat of whichever green you want -- Olive Green is close to Caliban. You're going to save a ton of money.
For comparison, this guy came out of the same box, but was primed and basecoat with an airbrush:
Both had a super thin coat of Caliban green brushed on with a 1/2 inch flat brush afterwards.