I am from the east coast so I am not familiar with exactly where the Colorado Trail is routed (though I seem to remember that it was more toward the south and west part of the state than in the front range). However, I did have a summer weather experience in the Rockies that may be of use. I was in Denver on business and decided to spend a few extra days out there exploring the front range. Since I was there on business, I didn’t have any gear with me so I just figured to do some dayhiking in my “regular tourist” clothes. Anyway, this was during the last week of June and temps in Denver had been 90+ all week so I assumed that weather would not be a problem. Needless to say, a front went through on my first day out, and I found myself caught in a very nasty snowstorm. I am not just talking up on the highest peaks either (though obviously they got it the worst). It was snowing all the way down into the foothills (but not quite to Denver). Thankfully, I was very close to my car when the storm hit because I highly doubt that I would have lasted very long in that weather in shorts, short-sleeve shirt and trail-runners. The point is that nasty weather can hit in almost any season in the Rockies, and you should pack accordingly. Better to have slightly overpacked and not need something than to underpack and find yourself in a tough spot and not have the necessary gear.
Ken G.