I can vouch for that. My unit was an 11H (anti-armor infantry) unit back in the rearly 90s and we had M901A1 ITVs and M113A2 APCs, so i would be lugging around a lot of those 5 gallon drums of hydraulic fluid and transmission fluid during field problems.
As for fuel we had mostly steel Jerry cans with the vehicle’s bumper number stenciled on them, along with the tan… Sometimes black, plastic water jugs.
Seeing that you are building a Canadian C2 MEXAS in Afghanistan , we deployed them in late 2006, our water cans as issued were black, fuel cans were green. I commanded all 4 types of C2 MEXAS and later Leopard 2’s, here is a quick reference photo from my second tour back in 2007.
I never came across any colored tabs nor any with “Diesel” painted on them for US fuel jugs. They were all the field drab/dark tan color with FUEL and 20L on both sides, like below. It was just assumed they contained diesel since we only had diesel engines in our vehicles and generators; a single fuel stream.
Also, note that the Canadian cans are different than the US cans. Their three-handle cans are marked POL, not FUEL, and the style varies as in this shot from eBay (look at lower left):