I plan on posting a lengthier report in the next couple days on my explorations of the Tualatin the past couple weeks, but for now...yes, those are coho! And no, they aren't all dark depending on where you catch them in the river. In fact, all of the coho I have closely encountered there this fall have been surprisingly bright. I would guess they finally start to darken as they get up to their spawning grounds in Gales Creek and other tribs/headwaters.
What to use depends on the spot you're fishing since the river can be fast cold riffles to deep slow jungle river, and everything in between. I've been concentrating on a deep slow hole in the jungly sections of the Tualatin, and have been getting all my action on spoons (green, silver, and pink). But, have only tried hardware, so can't say what bait would do if fished in the appropriate place. More to come in my report...
PS best bet would probably be before any more rain comes...gets muddy and full of leaves (at least where I'm fishing) pretty fast...remember only fishable through the 31st!