Where you are in the river, how late in the season it is, and what time of day it is all have some bearing on fly selection.
Early in the season (late July and through mid-August), the fresh run fish seem to like the bright flies (Dell Coopers, Purple Perils, Streetwalkers, etc.). The later in the season, the more fish seem to be attracted to drabber, slimmer flies. Also, the later in the season, the more effective orange seems to get. A Green Butt Skunk may be the fly of choice in early August, and the Max Canyon (a black, orange and white fly) in late August.
As the season progresses and the water temperature drops (late October through December), the fish definitely do not respond as well to the swung fly as they do to (gasp) nymphs fished off a strike indicator.
Start your day on the Deschutes as soon as you can see clearly enough to find the water. Under very low light conditions, a large, all black fly is effective (first thing in the morning and last thing at night). As it gets lighter, switch to one of the patterns suggested in the posts above. I would add an Ackroyd to my fly box, as it's been a very effective fly for me over the past several seasons.
Also, do not forget your skaters and wakers. The Waller Waker or any of the many Bomber variations (Purple with a red butt is good) really pull fish up.
When the sun gets full on the water, lots of people give up for the day, but don't. Switch to a sink tip and put on a big purple fly and keep after them. There's often a lull in the action between one or two in the afternoon until the shade comes back on the water, so it makes for a convenient siesta break.
Hope you enjoy your fishing on the Deschutes.
Cheers,
Eric