In other words, it's called leaf peeping or viewing the fall foliage, but since (as I learned last week during my trip out to ColRADo!) Aspen trees grow in groves and the the trees change colors at different times depending on the altitude they grow at, it's more like a hunt + chase to find Aspens that are at their peak golden color.
For example, I first arrived in the mountains in Colorado via Independence Pass and Aspen (altitude 8,000 feet), but the Aspens were only just starting to turn gold there. Womp womp. Let me tell ya, I thought I was gonna get skunked on my leaf peeping vacation! Feeling a little frustrated, I hopped back in the car, drove another 2.5 hours to a higher altitude in Breckenridge (altitude 9,600 feet), and then the gold, oh the gollllddddden Aspens!!!