The Colorado Department of Revenue site reports that a ticket for 10 to 19 mph over the speed limit is 4 points as you mentioned. As the officer told you, CO law will let a person who receives a citation for a violation such as this pay the fine and surcharge for the violation (on or before the date the payment is due) be assessed less points.

For a violation having an assessment of 3 or more points the points are reduced by 2. Whenever a municipality or county reduces a traffic offense, the reduced offense and points assessed for such a reduced violation shall conform to the point assessment schedule.

There are a few offenses that worth 2 point but it would appear from what the officer told you; in your area they reduce the violation to the 2 point offense of operating an unsafe vehicle.

Since there is an offense and points going onto your Colorado driving record, this violation could affect your insurance rates. The state of CO allows insurance companies to use your driving record as one of the factors they can determine rates on. Check with your insurance company to find out if this low point offense will affect your rates.

Another way to find out about your insurance company's rating system is to contact the Colorado Division of Insurance and request information on it since insurance carriers must file their rates with this insurance regulator.