So, an example of one way of doing this that I was thinking about:
Forgive the quality, took about five minutes, but it at least shows the general idea here.
So basically, those two planes are using the exact same diffuse texture, with a CC map for the different coloration, and a different normal map.
On the right you have a typical Forerunner panel. Gray(no change to diffuse color), and some Forerunner-looking lines on the Normal.
On the left, you have the SAME diffuse, but with the diffuse color changed to a more light brown-ish color(via CC map, RGB tint), and a normal map that makes it look more like...dirt or sand or something.
So, in theory you could do this, and give the player the option of having a Forerunner, UNSC, Civilian, Covenant look to the Forge objects like someone above mentioned, without actually having to model, UV, independently texture, tag, etc. a bunch of different pieces. Would take up less disc space, and RAM.
The only downside to this, is that you would then have to have more textures. A CC map for every Forge piece, and multiple different normal maps for each as well. So right now a typical Forge object might have something anywhere from 2-5 textures(diffuse, specular, normal, illumination, AO?), it could potentially go to 7 or more, depending on how they have stuff set up. So, even if Forge had say...50 objects, at 5 textures a piece, that's 250 textures JUST for the Forge objects alone. Adding the extra two would be an extra 100 textures. Textures are a pretty big resource hog to begin with. Adding to that would either hurt the game framerate wise, or they would have to accommodate for it by toning down the overall graphics of the game, just to make room for the extra textures.
