The Blue is really three or four different rivers.
First is the area just below the dam in Silverthorne. This is a very classic tailwater - gin clear water, runs-riffles-pools, and combat fishing. The rainbows here are very particular, but catchable. They feed on mysis shrimp from the lake above and are some of the most beautifully colored fish I have ever seen because of it. Sight fish these bad boys - 6X is the ticket. Mysis shrimp, small realistic baetis imitations, and maybe a parachute adams or two (very small).
The area below the town has a lot of private water, but you can find public access (remember that our access laws say you can own a stream bed - not like Montana) so be a little careful where you wade. The river widens and the fish are a little easier to fool ( a little). Again, this time of year is BWO and maybe Caddis time. Trout will feed in this are more on the surface than in town, but you will still catch more by nymphing - traditional beadhead mayfly and caddis nymphs will suffice. However, a san juan worm or a terrestrial might be just the ticket.
Above Silverthorne, you can access the river in Breckenridge where they have aquascaped a few miles just below town. The same fare as below Silverthorne works here. This is a big ski town, and any of the ski parking lots along the river are good places to access the river.
Downstream there is even another tailwater below Green Mountain reservoir that can only be floated much of the year due to high water and lots of private land. But when the flows there drop to about 300, you can wade a good stretch of it. They call this section Jurassic Park because of the prehistoric looking terrain and the huge (10-15 lb.) trout. No joking. Am 18 inch fish is quite common and a 25 incher can be found in lots of holes. In this section you chuck big, ugly stoneflies, pig stickers, worms, and egg patterns.
I would hit a local fly shop and buy a few flies and get some good up-to-the-minute information from them. Here is a decent link to a bunch of Colorado fishing information Colorado Fishing Network
Feel free to PM me in August or just before you come. I fish the Blue quite a bit from July to November until ski season really starts - the traffic on the interstate is just too crazy for me once it begins.