AdWordsAdvisor - 11:20 pm on May 27, 2010 (gmt 0)
Once in a thread like pretty much like this one I responded and guessed that folks were probably seeing a test, since Google tends to test stuff a lot.
Shortly thereafter I noticed a blog post saying something along the lines of "Google confirms that..." and linking to the thread with my post, here in the forum, to document that confirmation.
Since then, I've pretty much stopped guessing at what might be going on. ;)
Except that in this case, I'll say that (in spite of many tries) I have yet to any color other than the usual color that I always see, which is really hard for me to even name, since I am color-blind.