Actually with German armor you're not terribly far off, just expand the statement to include yellow and you're there.
I'd wager, (assuming they're just stock standard fuel barrels and not something mounted on the tank) that they're green as has been suggested, if they're to be mounted on the tank, try putting "mud" over them as it was a common practice for German crews in Africa to camouflage vehicles and objects in mud before repainting.
I'd also wager that troop's canteens and other objects were relatively untouched, too much work for too little gain.