SEOUL — South Korean rapper Psy wants his fans to turn up in white at his April concert where he will launch a new song that he hopes will cement the success of his “Gangnam Style” Youtube hit. “See this pic and let's be white on 0413”, Psy tweeted on his @psy_oppa Twitter feed on Wednesday, referring to the April 13 concert to be held in the South Korean capital of Seoul. The chubby rapper, who shot to fame with over a billion YouTube hits in 2012, subsequently poses in a variety of white clothing, ranging from a spacesuit to tennis whites and even a bridal gown and skimpy figure-skating dress.