I'd bring R1 long johns. At camp, you'll appreciate the extra warmth. When moving, as long as you have either wind or rain pants, you'll be warm enough with just shorts underneath. I'd also consider just bringing your schoeller pants - depends how lightweight they are, though.
For Colorado, it rarely rains more than a few hours, but it does so pretty predictably, almost everyday in summer, between the hours of 2pm and 6pm. The only exception I've found to this is when chance of precipitation in the area is greater than 40% - quite rare.
The combination of wind with the brief periods of rainfall is what makes you cold out here during the day, so if you have a typical forecast and wind protection you'll be fine without rain gear -- as long as you can pitch your shelter fast and can cook under it (so you can wear dry camp layers when you stop moving).
Also, make sure you're prepared for 20 degree nights. I've ran into a surprise low of ~14 in early June (forecast was 34 about 1500' below camp). This was with daytime temperatures in the 60s. Clear skies can sometimes make the temperatures drop a surprising amount.
My layering for 3 season alpine use out here is:
REI acme pants (lightweight schoeller)
merino wool briefs
merino wool long sleeve zip-top
merino wool liner gloves
merino wool buff (flexible balaclava, hat, earcover, towel)
montane windbreaker (hooded, can pull sleeves over hands)
As long as I'm moving, I don't get cold in the brief rain and high winds. I prefer merino wool since I've found it to be much warmer when wet, compared to synthetics (flash-off?). The REI acme pants can be a little warm (70+), but they're performance is worth the trade-off - durable, don't snag or flap in the wind, stay out of the way when climbing and are warm enough in strong winds during summits (and spring skiing at A-basin) down to about 40 degrees.
lightweight down parka (WM Flash)
lightweight down pants (WM Flash)
lightweight down socks (goosefeet)
I bring these because they're as lightweight as heavy baselayers (~16oz total), but they're MUCH warmer and can supplement my 30 degree quilt for the surprise record lows we sometimes get. I also like to wake up early (brrr) to catch sunrises and alpen glow for photography.
optional (only brought if precip forecast is >40%):
rain pants, jacket, shell mitts (~16oz total)