Colo. Rev. Stat. § 40-9-109
When an individual with a disability is accompanied by a service animal or an animal that is being trained as a service animal, as defined in section 24-34-301, C.R.S., for such individual with a disability, neither the individual with a disability nor the service animal shall be denied the facilities of any common carrier, nor shall the individual with a disability be denied the immediate custody of the service animal while riding upon a common carrier. The provisions of this section also apply to a trainer of a service animal, as defined in section 24-34-301, C.R.S., for use by a qualified individual with a disability, unless the service animal presents an imminent danger to the public health or safety. The individual with a disability or the trainer of the service animal shall be liable for any damage done to the premises or facilities of the common carrier by the service animal. An animal being individually trained for the purpose of aiding an individual with a disability shall be visibly and prominently identified as a service animal in training.
C.R.S. § 40-9-109