In the photo, the pop star matches her outfit to her new neon green dye job ... debuting a full rainbow center part that sharply contrasted against her waist-length black hair.

She wore a neon feathered skirt and matching hair ... Nicky Hilton Rothschild went full rainbow, wearing a snakeskin striped dress in primary colors. Her new sister-in-law, Tessa Hilton, also ...