When I met with Microsoft before the release of the Windows 8 Consumer Preview, I was told that the company originally intended to use a different Start screen color scheme for each milestone. (The Developer Preview was green, for "go".) Surprised by the negative comments about the single color scheme in the Developer Preview, however, Microsoft decided to allow several color schemes in the Consumer Preview. But the plan has always been for the final version to support many, many color schemes.
The availability of these new colors is apparently the theme, if you will, of a new post on the Chinese web site Win8China, which has been leaking Windows 8 goodness for months. Not a big deal, and not unexpected, but apparently the first leaked post-Consumer Preview build does include new colors.
The new colors in Setup
The new colors in PC Settings