Colon Panama is on the Caribbean entrance to the Panama Canal, and is a rather impoverished/industrial area. Ironically, it was founded by Americans prior to the the building of the Canal, but most have long departed. However, we did find an American expatriate still running a t-shirt shop in the port area.
Like many countries, there is no set taxi rates, so negotiate with the driver prior to entering the cab, or you may be in for a shocker when it comes time to pay the fare.
There are many canal oriented excursions available, but if you wish to just hang close to the ship, you should limit your adventures to the immediate shopping port area, called "Colon 2000". The street vendors are generally pretty aggressive, and and offers for tours are almost like running a gauntlet as you try to enter the few shops in the port area.