Umanets said he was not a vandal: "Some people think I'm crazy or a vandal, but my intention was not to destroy or decrease the value, or to go crazy. I am not a vandal."
Umanets, who studied art, is one of the founders of "Yellowism", which he describes as "neither art, nor anti-art". "Yellowism is not art, and Yellowish isn't anti-art. It's an element of contemporary visual culture. It's not an artistic movement. It's not art, it's not reality, it's just Yellowism. It can't be presented in a gallery of art, it can be presented only in a Yellowistic chambers.
"I am a Yellowist. I believe what I am doing and I want people to start talking about this. It was like a platform. I don't need to be famous, I don't want money, I don't want fame, I'm not seeking seeking attention."
He said he did not plan which painting he would write on, but thinks he found "the perfect choice", and said he feels he may have increased the value. "To be honest, I do believe I increased the value. It seems probably ridiculous for someone but I do believe in this. I didn't decrease the value, I didn't destroy this picture, I put something new."
The gallery said it does not have a price for the defaced piece, but paintings by the Russian-born artist often fetch tens of millions of pounds. Earlier this year, Rothko's Orange, Red, Yellow sold for £53.8 million - the highest price paid for a piece of post-war art at auction. The 1961 painting went under the hammer at Christie's in New York.