As has been discussed at great length many times before, the Protec paint is the correct colour.
The reason why the green on the vehicle is much lighter is because it has been exposed to many years of weathering and has faded.
Generally, with paint, the base fades (or is changed by weathering and sunlight). (You can confirm with your Watyl expert.) What this generally means is if you get paint made up to match the lighter faded colour, the matched paint will fade even lighter again.
You now can chose what you want to do. What ever you do, you will get diferent colours. Either be happy with that or repaint all the olive drab bits in Protec.