I cannot work when sad. For my art I need hope, and that gives me inspiration and energy and ideas.
I think much art, especially American, especially African-American, comes out of a Blues mentality --- but NOT 'melancholy' as thought of in the past!
Dr Cornel West describes himself as a "Bluesman in the life of the mind, and a Jazzman in the world of ideas."
I feel similarly, I am a Bluesman of the mind, a RocknRoller of painting, a sequential-artist/comicbook penciler of art history. West is an amazing inspiration to me.