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Take your atv's vin # to your local DOL and just buy the tabs.
It depends on where these "green dot" roads are. Is this on National Forest, or is it on WDFW land? If it's on National Forest it's probably not legal to ride an ATV there at all. If you're talking about WDFW land, then it might be legal, if it isn't posted otherwise. I don't know of any law about riding double. Although every 4 wheeler I've ever seen will say right on it that it is NOT meant to carry passengers.
a road isn't open for ATV use just because it is a "Green Dot" road.