Katy Perry ascended the red carpet at the annual Costume Institute gala looking like the bride of Frankenstein in her red John Galliano dress and veil. Jennifer Lopez wafted by in sky blue Valentino, flanked by her favorite Yankee of all time and the founder of the design house responsible for making her gown. By contrast, the entrance of the private equity guru Stephen A. Schwarzman and his wife, Christine, was inconspicuous. Nevertheless, journalists called out their names. Cameras continued to flash.