I have been grinding all week just to get the ultimate, only to realize it is only for the mark VII armor. universal colors would make it worth actually trying to do this and give us more customization options.
As an edit:
I think that all armor pieces should be interchangeable between each armor core (except the base armor pieces for each core) that way our spartan can really be our own instead of just the same pieces for the same sets. Ive seen it so much, and maybe its just cause its early in the game, but there is very little personalization to each spartan. The interchangeable armor pieces would help with that.