Mark Rothko, 1951. Subject of the largest private art transaction ever — $186M in 2014.
From Wikipedia
No. 6 is a painting by the Latvian-American expressionist artist Mark Rothko created in 1951. In common with Rothko's other works from this period, No. 6 consists of large expanses of colour delineated by uneven, hazy shades. In 2014, it became one of the most expensive paintings sold at auction.