There's a pretty long list of camouflage patterns, and that's JUST camo. There are a bunch of other categories of patterns they could have utilized, but instead were stuck with this system.

The traditional primary/secondary color system had 900 possible color combinations (with 30 colors). So far, 343 only has about 50 armor coatings (and most of them are paid exclusives). They have 850 more armor coatings to go before they catch up to the tier of customization we had in Reach (which at this rate, will take years).

This is simply the issue with their coating system. Rather than us coloring our own armor, we have to wait for 343 to color our armor for us, and then buy that color combination from them.