Even a day hike on the Colorado Trail is high-level hiking, and extra precautions and information are going to get you through. Fortunately, more bridges and markings are added every summer. Research your trail section before you go, paying special attention to the elevation. Individual trails have elevation gains ranging from 1,040 to 4,520 feet (317 to 1,378 meters), so choose appropriately. The hikes may take you to remote and snowy mountainous areas, so don't hike alone if you don't have to.
Regardless, always file a hiking plan with friends or family, so somebody back home knows where you are if the worst happens. Take a cell phone to call for help, but be advised that service is not consistent along the Colorado Trail. (However, they do work better in high, open areas, such as on the peaks of passes or ridges.) Wear wool or synthetic clothes (and multiple layers of it), as cotton doesn't insulate if it's wet. And as with any trek, pack extra clothing, food, and water, just in case. And when in doubt, there's always more information available at local ranger stations.
There's also more information on hiking trails on the next page, so head over there if you're ready for the journey.