And by dyeing I'm referring to the skill of adding color to an object. Some games have this option, but many games don't. The most common reason I've seen is that they don't want players to mess with their carefully crafted artwork. But this is obviosuly something that the players desire. Just look at the number of complaints on the WoW forums about the color choices for some of the raid armor!
Here's how to do it right, and better.
First off, as you're designing the textures, they need to be layered in a consistent manner. That way, when you implement the 'dye armor' feature, you can specify which layer gets dyed, and thus have more control over how the players affect your artwork. Secondly, allow multiple layers to be dyed independently. This would allow the players to do things such as give the armor a 'wash' (altering the color of the grooves), 'overbrush' (color the peaks) or 'stain' (alter the basic color of the armor). You could even go so far as to allow color layering (IE, the current color affects the results of your dye job) to give the players even more subtle nuances about how their armor looks.
Not only would this provide simple customization options with little overhead to the company, but I could also see an in-game economy springing up around the Dying profession as some players would have much more interest and skill in creating nice looking outfits.
One disclaimer. Don't give players access to a pure black dye option. It just looks like crap.