It doesn't look like it is rotating so much as continually being reflected across some y-axis - which it is - but I suspect that isn't your ultimate intent. I suggest inserting some frames where the lines that divide the colours are in different places.
This post by baccaman21 might be of interest to you. http://www.wayofthepixel.net/pixelation/index.php?topic=5201.msg62325#msg62325 Zounds! I can't seem to add links.
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and thanx again for the web site it's really helped.