The last day to register is 29 days before the General election. The subject of absentee voting is confusing to a lot of people, but the rules are pretty straightforward. Any registered voter may apply for an absentee ballot. The application for an absentee ballot may be obtained from your County Clerk no later than the close of business on the Friday immediately preceding the election. An absentee ballot must be returned by 7 p.m. on election day to a place designated by your county clerk.
Early voting is another option.
Each county in Colorado provides early voting polling places. Anyone who is registered may vote in person at locations designated by the county clerk 15 days prior to the General Election. Early voting ends on the Friday preceding the election. Call your county clerk if you have specific questions about locations and times. The belief that only one person with just one vote can't make a difference is probably the most common of all reasons people stay away from the voting booth.