Using Microsoft's IE specific CSS filter's, it is possible to set the bg-color of the ad to transparent so that any textures or images show up through your ad. Is this a violation of the TOS? I haven't modified the javascript Google provides, I've just been smart about my css styling.
Check http://www.after5webdesign.com/pldtemplates/index.php?tplselect=Woodland It can be done. That template is not finished yet, but it will demonstrate the concept.
I can't see a problem, but for the safety of your account I think you should ask the big G. Personally, I think it looks good. It doesn't display any intention to cheat.
Always good to ask I suppose. I just hate dealing with Google's Support. This isn't the first time I've found something kinda cool that involved Adsense, and it took me several weeks of emails to get the uneducated adsense support lackey to even understand the question before I could finally get a correct answer out of them. It involved using adsense code in CDATA tags from a private admin panel to create an XML feed that updated another page on a different domain I owned. Thus abc.com/private_rss would update xyz.com/public_page. The eventual answer was no, even though both domains were owned by me. I could have done it anyway since there is no way Google would have been any wiser (the public page has adsense already), but I like the few pennies that adsense generates for me.
I would think that if it involve direct or indirect manipulation of the Adsense code it would be ruled a violation. That said, as recommended, it's always prudent to as the big boss G.