If you have the original box, it may show a notation about optional grips on the end flap. Also, if you have the gun "lettered" (order a letter from the Colt factory, which describes the gun's configuration as it left the factory) it may list optional factory grips being added. I have seen at least a few new Colt handguns with Pachmayr grips that had the Colt "dancing pony" medallions on the side, so I do believe there was such an option for some models. For a collector, though, you have to have something to "prove" the grips are factory options vs. user- or dealer-installed.
Almost everyone likes the "look" of the factory wood Colt revolver grips, but most people I know that have shot with them, dislike how they feel in the hand, especially in the harder-kicking calibers. I'm a big fan of functional rubber grips; I know they often look like crap compared to nice wood grips, but I'm generally a "function over form" kinda guy.