If after filing your Colorado income tax return you find you owe state income tax rather than mailing a check, you can pay using our electronic check or credit card Online Tax Payment service. This online service includes an administrative fee. For credit card transactions, the administrative processing fee is the amount due plus $0.77 multiplied by 2.25%. If you choose to pay with cash in the form of an echeck, the administrative processing fee is discounted to $1.00 per transaction.