Liberace has been gone for, lo, these many years, but Las Vegas has a flamboyant new piano man. It's Elton John, who launched a three-year run at Caesar's Palace on Friday. His show, dubbed ''The Red Piano'' after the lacquered Yamaha grand he plays during the performance, is scheduled to run at least 75 shows in Caesar's Colosseum, the 4,100-seat hall built for Celine Dion's show, now in the second of its three years. (John is basically the fill-in act when she takes time off -- not too shabby.) The concert consists of some 15 of John's hits backed by a multimedia extravaganza of lights and video that was designed by celebrity photographer David LaChapelle. Those in attendance for Friday's opening night, according to the Associated Press, included Michael Douglas, Catherine Zeta-Jones, Barbara Walters, Joy Behar, Pamela Anderson, Christina Aguilera, Kathy Griffin, and Sharon Osbourne, who was no doubt planning an eventual Vegas engagement for Ozzy.