There is no law giving any employee in Colorado the right to inspect personnel files.
If you have a union, you have many more rights. Your union contract may give you additional rights to review your file, have copies, or remove unfair information. Ask a shop steward or representative. Personnel files can almost always be reviewed during a grievance or discipline. Information in your file can be very important during discipline or promotion.
How to ask for your files: Since you do not have the right under state law, first investigate if your employer has a policy that employees can review their personnel files (check your employee manual and ask other employees). If there’s no policy which says employees can review their file, it’s still worth asking. It may be best to ask verbally (maybe you’ll be allowed to review your file without the person you are asking checking for approval). Decide who is most likely to let you see the file, probably either HR/Personnel or your supervisor. You can also read “How to Review Your File and What to Expect."