Rainbow effect will stick around especially if its skin oils.
Any moisture causes it really. Ever sneeze near a television or your monitor? Light refraction through moisture causes the "rainbow effect"
Now as for my advice, this will happen on any glass screen but you can control the cover.
ZAGGs keeps the moisture on it more, and its harder to wipe off..it smudges more than anything.
I just returned mine, I suggest you ask yourself if you still like the IS after several days of dealing with this.
I would suggest a dry install shield, I myself got a Power Support Crystal Set, and it works sweet, feels like a stock screen (as close to it) and whenever I get this streaking, it goes away very easily wiping it against some cloth preferably microfiber.