I'm fairly certain the .67 is camo and is no stronger as the extra weight is ink. The .75 is the next stronger material but obviously isn't printed so may not be as dark.
Printable View
Like Stocky mentioned above, the Dyneema Composite Fabric (formally Cuben Fiber) used in ZPacks Duplex tents is .55 oz/sqyd in the standard configuration. If you choose spruce green or a couple of the other colours it's .75 oz/sqyd. DCF is constructed of a grid of white Dyneema filament threads and then covered by a transparent membrane. The difference in weight for the spruce green option and others is attributed to a higher Dyneema thread count making it more durable and slightly less see-through. The camo version in the .67 oz/sqyd on the other hand is heavier due to the membrane being printed. It doesn't actually have a higher Dyneema thread count from my understanding, but does reduce the see-through nature of the fabric even more so than the .75 oz/sqyd options. I don't think ZPacks is offering the camo version option any longer.
Joel