I can't imagine making a certain color only have the upgraded size. What's the point? "Let's make a large portion of our customer base unhappy by forcing them into a color they may not want just to get more storage space." "Yeah, sounds like a great idea!"
With the new 120 and or 60fps video modes a 16gb iPhone would be crazy small. So I really think they are going 32/64/128, with the 5c taking on the entry level 16gb as it will not have the 120fps mode.
But outside of that I wouldn't put it past them to make the Gold a 128gb only model, but that wouldn't be smart if you ask me.