I would suggest the San Juans as others have. Iconic trophy view from the summit of Dallas Divide. Color was unbelievable 2016, somewhat disappointing in 2017. I usually plan my fall trips there around the fall color in the San Juan’s and fill in the other destinations secondarily. Do not forget Last Dollar Road above the airport near Telluride, at least the lower part (Barns, Mnt Wilson, aspens). Also county roads 5,7 and 9 off of 62, esp. CR7. South of Ouray to Silverton(Red Mtn area), nice views from hwy 550 incl. Yankee Girl Mine.
Other possibles include Crystal Mill out of Marble and Maroon Bells if the color is compelling enough to rub elbows with 2 or 3 hundred of your closest friends at sunrise. Martres Vol 3 Photographing the Southwest, IMO, is a must have investment for the trip you describe. There are easily found on line guides for Colorado color as well.
I found that Garden of the Gods and Black Canyon to not reach my expectations although I did get a fabulous misty canyon photo upon entering the Black Canyon park that was gone in 5 minutes. (Drive by shooting at its best😉). However, Matt’s images of the canyon are among the best I’ve seen. I enjoyed walking through Garden of the Gods more than photographing it. If into abstracts, the Sand Dunes in east central Colorado can drive you crazy(you’ll get plenty of time with your healing brush unless you arrive after a strong wind).
Hope the color treats you well.