Colorado requirements for residency are as follows:
Colorado law states that, upon establishment of residency, you have 90 days in which to register your vehicle
Gainfully employed in Colorado.
Own or operate a business in Colorado.
Reside in Colorado for 90 consecutive days.
College students, temporarily residing in Colorado and claiming another state as their residence, may retain valid out-of-state plates.
Military personnel, on active duty in Colorado and claiming another state as their home state of residence, may retain valid out-of-state plates.
Non-residents employed in Colorado who commute daily from their residence to their place of employment within Colorado may retain valid out-of-state plates. This is restricted to only those states entering into a reciprocal agreement with Colorado (Utah, New Mexico, Wyoming, Kansas and Nebraska)