Colours - Maximum 12.
Transparency - No.
Animation - No.
The forum will have a template of all 12 months for you to use as a reference.
You may use a template for your entry or make your own version, but it must stick to the template size.
Anyone creating all 12 calandar pages will be awarded with a 'gold star' in their profile, in addition to the ribbons (quality and effort counts). 
The challenge thread will have all the challenge updates. The thread is also a great place to post your WIPs.
interesting challenge. are we allowed to tune up the template a bit, like other font/fontcolor, background color, red-letter days etc. ?
*edit (read carefully, stupid =)
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But now it would be odd.