I've used Zagg InvisibleShield protectors for years on all my electronics (except my e-ink readers). I've never noticed my colours to be dramatically dimmed, nor have I had a problem with rainbows. I've put the things on my phones, GPS screens, camera LCD's, even on a watch face once.
The nice thing now for me, is that there are Zagg kiosks in West Edmonton Mall, so I don't even have to apply the film myself anymore!
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http://www.zagg.com/invisibleshield/index.php)