The Sherman Firefly was a World War II British variant of the American Sherman tank, fitted with the powerful British 17 pounder anti-tank gun as its main weapon. Originally conceived as a stopgap until future British tank designs came into service, the Sherman Firefly became the most common vehicle with the 17 pounder in World War II.
The next stage is base coat for the underneath of Humbrol Dark Green. This will add shadow and depth to the main (top) base coat of Warpaint British Armour.
As you can see from the top view, the white undercoat is still mainly visible.
See the workbench feature on my Flames of War Sherman Firefly VC.