I'm getting a lot of traffic to this post from last year about "Madonna's new look." I'm sure it's because people are Googling "Madonna's new look" because she has a new new look. I love the new cut. It's something you could move about wearing in the real world, not like the hairstyle it replaced, the retro Valerie Cherish thing that would require you to have Mickey scampering after you everywhere, touching it up constantly.
As for the new color. Use your judgment. Doing the roots every week could get expensive... and boring.