Are you required to put a DUI on a job application if the DUI happened 8 years ago in Colorado?

If you were arrested, convicted and sentenced, you had better. Especially If you are applying for a CDL, anywhere, you had better disclose it because they will check all interstate DMV records. In this day and age of computerized records you very seldom can get away with not disclosing the information. Best thing to do would be to ask the prospective employer if such information would be relevant. An old DUI arrest may not be of any interest to them for whatever job you're seeking.