In Carlson v. McCoy, 193 Colo. 391, 566 P.2d 1073 (1977), a lease agreement was signed between the parties that was silent as to whether the landlord could keep the tenant's security deposit at the expiration of the lease. After the lease was signed, however, a statute became effective which addressed a landlord's willful retention of a security deposit and allowed for treble damages against a landlord for violation of the statute. After the lease ended, the landlord withheld the tenant's security deposit and the tenant then sued, relying upon the protections afforded by the statute. The landlord defended on the ground that at the time the lease was signed, the statute was not in existence and that the statute therefore affected his rights. The supreme court upheld application of the statute to the case, concluding that although the lease agreement was signed before the effective date of the statute, the tenant's right to recover the security deposit did not arise until the end of his lease term, which occurred after the statute was passed. See Carlson v. McCoy, supra.