Williams playfully chases her daughter Matilda, 3, down the street in Brooklyn, N.Y. Plus: Rihanna, Gwen Stefani, Brad Pitt and more

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COLOR-BLOCK PARTY

Katy Perry gets first-class treatment from a group of brightly-dressed flight attendants at the Vienna International Airport in Austria, where she's a special guest of the annual Life Ball, Europe's largest charity event dedicated to the fight against HIV and AIDS.