Nicole Richie and hubby Joel Madden hit up Kate Hudson's big Halloween bash Saturday night, where Nicole paid Halloween homage to a certain diva -- Ms. Jennifer Lopez!

Nicole, 30, sported Jen's signature hot pink track suit, sunglasses, bun and hoop earrings. Adorable!

She and Joel had a signature phrase this Halloween: "Happy Harloween," which Joel Tweeted several times over the weekend. The phrase, of course, is in honor of daughter Harlow, 3. The couple also has son Sparrow, 2. Wonder what the kids will be for Halloween!