You should also know there are lots of frauds or counterfeit guns out there in the event you plan on investing. Sometimes, a small detail change can transform a gun of average value to one with a high premium. Likewise, altered guns can suffer greatly in value. Last year on Pawn Stars, customer came in with "antique" handgun he had paid over a thousands bucks for, hoping to turn a profit. Gun proved to be an Italian reproduction cleverly aged to look authentic 19th century. Gun was only worth what it originally sold for, if that much.
Regarding Colts, thre are lots of books out there and you should seek out anything written by R.L. Wilson.
Int'l Assoc. of Law Enforcement Firearms Instructors