Just got back from there. My group and I have been going to Colorado (Taylor Park, Ouray, Telluride, etc.) for 13 years. My feeling is the latter part of August is best. We were there from the 14th of August through the 28th. The weather was actually quite nice with a couple of days producing some intermittent showers with hail and a little dusting of snow. Otherwise, sunny and reasonably warm. Some years are wetter than others, as was last year when it rained pretty hard some days. Usually, you can expect afternoon showers. Just be prepared with the waterproof jacket and you should be alright.