Having worked in the Rockies in every month of the year, I can guarantee that camping and sightseeing in the Colorado mountains in October beats May every year. Just a couple of reasons: Trail Ridge Road in RMNP never opens before Memorial Day weekend due to snowplowing, but lately has still been open in early October, and USFS campgrounds at higher elevations and some beautiful state parks generally do not open before mid- to late May.
We camped in the Ridgway-Lake City-Gunnison area in early October last fall in gorgeous weather and with aspen in Lake City and on Monarch Pass still at their peak. The first weekend in October 2016, the aspen along Colorado 17 on Cumbres and La Manga passes was the most beautiful fall color I have ever seen in my 55 years in Coloado! In May, those aspen won't even have leaves yet.