As of at least 2007 Google has been pushing design tests to designated users. The new Google layout you see is nothing new, it has been appearing intermittently in searches, though substantially less polished. As you can see here, the contrast between the 2007 version and the 2010 version is in the visual design, while functionality remains largely unchanged.
Additionally, Google has taken steps to redesign their logo (right).
Having read an article years earlier, which I do not have time to research and link back to, I can speculate with certainty that a long time (months) was taken on simply deciding the strength of the bevel or the tone of the blue (or green, red).
For further reading check out the official google blog.