Colorado Revised Statute 18-12-203-VI

VI - A training certificate from a handgun training class obtained within the ten years preceding submittal of the application. The applicant shall submit the original training certificate or a photocopy thereof that includes the original signature of the class instructor. In obtaining a training certificate from a handgun training class, the applicant shall have discretion in selecting which handgun training class to complete.

As taken from the Jefferson County website -
Where can I get a firearms training certificate?
A firearms training certificate can be obtained through any NRA, gun club, shooting range or weapons training facility that has a "certified instructor." You can verify the instructor is certified by their credentials. If the instructor is NRA certified, they will have an instructor's certificate as well as a wallet-sized card which shows an expiration date. If expired, the instructor is no longer allowed to be teaching classes. Once you have decided on a facility to receive your training through, you will need to obtain the following required item from the certified instructor to be submitted with your application:
  • A training certificate that includes: (your name, course name, date of course, and the instructor's original signature);
A "certified instructor" is an instructor for a firearms safety course who is certified as a firearms instructor by a county, municipal, state, or federal law enforcement agency; the Colorado POST board; a federal military agency; or a national nonprofit organization that certifies firearms instructors, operates national firearms competitions, and provides training, including courses in personal protection, in small arms safety, use and marksmanship.
A "handgun training class" means:
  • A law enforcement training firearms safety course;
  • A firearms safety course offered by a law enforcement agency, an institution of higher education, or a public or private institution or organization or firearms training school, that is open to the general public and is taught by a certified instructor; or
  • A firearms safety course or class that is offered and taught by a certified instructor.
If you have doubts, contact your local Sheriff and find out if they will accept it as training.