The color schemes of LayerVault and FlatUI are also almost identical. http://pixxel.co/feed/layervault-issues-dmca-takedown
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.
And besides, establishing an infringement of trademark and that it was then infringed will require an absolute mountain of cash and lawyers and time. I'm assuming they have nothing relating to the IP they're annoyed about on paper and so they'd need to show that they 'owned' it in equity. They'd almost certainly go bankrupt before they have a chance of winning a case in court.
(IANAL... yet)
The only thing you can file a DMCA takedown notice for is a copyright issue. That's it. By filing a DMCA takedown notice you are asserting there is a 'copyright issue'.