You may be required to file an SR-22 when you reinstate from specific suspensions and/or revocations. The SR-22 requires the insurance company to notify the DMV of any policy cancellation. The SR-22 form is not an insurance policy.
If you don't keep the SR-22 current, the insurance company will notify the Motor Vehicle Division that the SR-22 is no longer in effect, but is still required. Your driver license will be suspended for that reason alone.
When you purchase liability insurance, the insurance agent can provide the SR-22 form. When the liability insurance with the SR-22 rider is purchased, the form must be filed with the Colorado Division of Motor Vehicles. You may upload the SR-22 form at MyDMV.Colorado.gov. (Find the View/upload reinstatement documents link near the bottom of the Driver/ID Services tab, or you may mail it in with the Application for Reinstatement (Form DR 2870) and any other requirements necessary for reinstatement.
If you decide to change insurance companies, you must get a new SR-22 filed before the old one expires.