If Colorado was your home of record when you joined, you later took legal residence in another state, and you now reacquire Colorado residency, you can subtract the active duty military pay you receive after reacquiring residency from your Colorado taxable income. You do not have to be physically in Colorado to reacquire residency, but you do have to show you intend to.
There is nothing to file in advance. Do one of the qualifying acts that shows intent, then claim the subtraction on your Colorado return.
Proof of the act you used to reacquire residency, such as a Colorado voter registration, a deed for Colorado residential property, a Colorado vehicle title and registration, notice to your former state, or a new will naming Colorado, plus your military pay records.
