According to Wikipedia, Mondrian developed his grid-like abstract painting style in the 1930's. While they weren't patented, they were created prior (faaaar prior) to the Windows 8 phone. Prior art, people!
Given the absurdity of present-day patent law, might we see Mondrain's estate suing Windows?*
* We're joking, of course, but it's a funny thing to think about.
(Hat tip: Stephen Levy on Twitter)