Assigning a value will be difficult.
While Colt made many commemorative models of guns, they also would make "private issue" models.
As I recall, the minimum order was 25 guns, and they would make up guns as fancy and ornate as the buyer could pay for.
These private issues guns were made for clubs fraternal organizations, police unions, police department commemorations, companies for executive gifts, and a rich person who wanted to give his friends a nice gift.
In short, anyone with the money to pay.
Since these were private issues, most of them are unknown even to Colt gun collectors.
Value would depend on how many were made, how ornate, whether the original box, papers, and other items that came with it are present, the organization it was made for, and the condition.
Several possible sources of information would be Colt themselves, and possibly Cherry's.
For Colt, you'll have to buy a Colt Historical Letter. This will detail when the gun was shipped, how many were shipped, and to WHO it was shipped, along with any special features such as engraving, custom grips etc.
http://www.coltsmfg.com/archive.aspx
Cherry's is a company that specializes in commemorative Colt's and may know some details.
http://www.cherrys.com/
For possible evaluation on actual value, you might contact the Colt Collector's Association:
http://coltcollectors.com/