Sounds like a perfect location for Thuja occidentalis or Thuja plicata. I can't think of many other conifers that do well in shady, moist, acidic areas. Does the area get a couple hours of direct sun, or is it mostly filtered? If direct, you could consider some of the nice gold colored cultivars, but it sounds like, based on your description you probably should just focus on the greens, as the yellows will likely color correctly in such little sunlight. You mention a 10 year maturity of about 10ft, but do not list any width constraints.
Here are a few ideas:
- Thuja occidentalis 'Degroot's Spire'
- Thuja plicata 'Whipcord' (very unique)
- Thuja occidentalis 'Pendula'

Others can probably come up with a lot better cultivars, those are just a few I am familiar with.

Good Luck

This post was edited by SC77 on Sun, Sep 15, 13 at 20:33

If you are near Seattle you are in USDA 8. One of the bluer named forms of mountain hemlock might be the kind of thing you are looking for. Or just a wild collected seedling of the typical species that has blued up nicely after being in the lowlands for awhile, as often happens with this species. Such examples look great with red, orange or yellow fall color - the old cool + warm color combination.

I would want to know exactly how much direct sun you would receive. In the PNW, even in midsummer our sun is not very intense and in winter so low on the horizon as to be pretty much ineffectual. IME, the vast majority of conifers are not very happy under such low light conditions - they become leggy and reach for the sun, the foliage dies off on the shadiest sides and in the interior and they just look generally unhealthy.

There are a bunch that could tolerate some light shade but I'd really like confirmation of available sunlight to make specific recommendations. Also, how moist is moist? Winter rains moist or all season moist?