If you are planning on having a really dynamic trip in which you can get the chance to visit the most important objectives in Colorado rather than to travel to a mountain resort and stay there for a week, then it is crucial to have your personal transport (not that other options are excluded, but it would be way more troublesome to plan your trip and you would have much less flexibility).
Colorado gained fame of one of the most beautiful states. There are high mountains, deep lakes and unique nature parks there. There are sites that one undoubtedly has to visit during the lifetime.
Colorado also hosts ones of the most famous ski resorts. In Vail and Aspen are situated well-known vacation spots. Any place in Colorado is possible to be reached by car. It is possible to use a private car or to rent an auto in Denver for example.