Under Colorado law, you do not need to have the power of attorney witnessed or notarized. Given your situation and the need for a loan, however, at a minimum you’ll need to notarize the power of attorney.
The law reads as follows:
“A power of attorney must be signed by the principal or in the principal's conscious presence by another individual directed by the principal to sign the principal's name on the power of attorney. A signature on a power of attorney is presumed to be genuine if the principal acknowledges the signature before a notary public or other individual authorized by law to take acknowledgments.” Colorado Revised Statute § 15-14-705
Having said that, however, it is best practice to have the document signed, notarized, and witnessed by two witnesses. This is because the signature is presumed to be genuine if notarized, notarization will be required in a real estate transaction if recorded by the agent (I assume your case based on your question), and if you try to use the power or attorney in a different state, the execution requirements to make a valid power of attorney may also require witnesses. Finally many financial institutions will be reluctant to accept an unacknowledged (non-notarized) power of attorney and there is no penalty if they do not.