Colo. Rev. Stat. § 38-12-802
Upon receiving any payment made in person by a tenant with cash or a money order, a landlord shall contemporaneously provide the tenant with a receipt indicating the amount the tenant paid and the date of payment. If the landlord receives a payment that is not delivered in person by the tenant with cash or a money order, if requested by the tenant, the landlord shall, within seven days after the request, provide the tenant with a receipt indicating the amount the tenant paid, the recipient, and the date of payment, unless there is already an existing procedure that provides a tenant with a record of the payment received that indicates the amount the tenant paid, the recipient, and the date of payment. A landlord may provide the tenant with an electronic receipt, unless the tenant requests a paper receipt, in which case the landlord shall provide the tenant with a paper receipt. For purposes of this section, a receipt may be included as part of a billing statement.
C.R.S. § 38-12-802