One game I've played over the years, in order to maximize my aspen color experience and to stretch out the season, is to do an aspen hike up north (Steamboat, RMNP) to 10,500+ feet around September 10. Then, each successive weekend, hike to a slightly lower elevation as the colors develop there. After a few weeks, the aspen at ~7500' start changing. That's about the time I will head further south (Sangre de Christos, San Juans), where the color change happens a bit later than up north.
However, it seems that this year the color is going to be delayed by a week, maybe two. My buddy and I were at 10,800' last week up the Middle St. Vrain drainage in the Indian Peaks, and there were zero aspen colors. I'm thinking that the peak might happen about October 1-10. If you can only manage one hike, I think the above suggestions would be stellar. And don't forget about the areas around Summit County, Vail, and Leadville--they have some nice aspen groves, and they're close (if you live in the Front Range).