Summary - Green Mountain can be a short hike from a parking area right below the summit or a longer hike from the road below. The drive up version is possible on Saturdays and Sundays from 9:00AM to 6:00PM through a gate on NW Holly Road at (47.59245, -122.83445). The drive is Priusable, at least in good weather, and ends in a parking area with a vault toilet below the summit. A NW Discover Pass is required to park. The vista - which is not the actual summit but in the AZ - has good views, trees to hang a wire, and picnic tables. ATT digital service was good for spotting. I didn't turn on my HT so can't comment on APRS. An easy drive, short hike, and nice spot for an activation.
Long Version - I did Green as a drive up so I would have time to hike Gold Mountain (W7W/RS-072), too. There are two ways to hike it, Wildcat, starting at (47.60056, -122.78849) and Gold Creek Trail, starting at (47.55108, -122.82731). The latter is also the start for the Gold Mountain hike. To do the drive up, look for the gate at (47.59245, -122.83445) with a sign that says it is open from 9:00AM to 6:00PM on Saturday and Sunday. I arrived at 7:30AM to find the gate already open, so up I went. The five mile long road is Prius friendly and the parking area at the end holds ten or twelve cars. You will need a NW Discover Pass to park. From the lot, it is a short hike up to the vista area, which is in the AZ. The actual summit holds a communication facility and is fenced.
The vista area has three or four picnic tables and a fenced viewing spot. A little lower is a large, new picnic pavilion. While I had the place to myself, the view to the west of the water and mountains, installed amenities and limited access by car suggest this place may get crowded, at least later in the day.
There are plenty of trees for hanging an antenna near a couple of out of the way picnic tables, so this might be a good place to park yourself for an hour or two, at least when the weather is fabulous like it was today. I didn't turn on my HT, so I don't know whether 2M is easy or hard or whether APRS works well.
Overall, an easy almost-drive-up, at least on a Saturday or Sunday, with good views and a comfortable operating position. Combine it with Gold Mountain, which has almost none of the above for a two summit day.