Let's add some google colors in this comparison http://cl.ly/NO8C
If it were ONLY the colors, or ONLY the look and feel of the widgets (which, come on, are almost exactly the same as well), or ONLY the icons… different story entirely. But it's the SUM of all of those things.
This is not how copyright works.
To me it seems like more of a trademark/trade dress issue, which as far as I know doesn't fall under copyright, but it's extremely silly to say that the resemblance between FlatUI and LayerVault isn't uncanny.