WASHINGTON — Perhaps adapting to the give-and-take of D.C. politics, Johnny Cash made a concession even before testifying before a House subcommittee Wednesday: The Man in Black wore white.A little, anyway. The country icon, clad in a white shirt and customary black suit, was there to speak in favor of two international copyright treaties. Cash, who has written 400 songs and recorded 30 albums, urged members of the House Intellectual Property Subcommittee to approve two World Intellectual Property Organization (WIPO) treaties that he said would give his songs important copyright protections on the Internet. Cash noted that he started his recording career in the 1950s when cyberspace was not even the stuff of science fiction. “We’re not recording on vinyl anymore. We’re recording on computer disks where there are hundreds of songs for the taking. We’re a digital industry, and music is changing hands at incredible speeds. Push a button and it’s gone,” Cash said. The Beltway visit wasn’t entirely business: Just 12 hours before his testimony, Cash received a standing ovation from Congress members and their staffs at an invitation-only performance at Ford’s Theater. The event, sponsored by the Recording Industry Assn. of America, drew hundreds of influential Beltway insiders, including Sens. Charles Robb (R-Va.), Pat Leahy (D-Vt.) and John Warner (R-Va.). With the WIPO treaties in the balance, Cash is one of a steady stream of performers whom the RIAA hopes to bring through Washington to lobby Congress. But Courtney Love probably doesn’t need to start packing her bags.