Britney Spears joined her new X Factor team at a party to celebrate the upcoming season in Central Park last night. Britney changed into a short purple Alexander Wang frock after wearing a white minidress for the official announcement of her involvement earlier in the day. Britney, Demi Lovato, Simon Cowell, and L.A. Reid will be judges on the reality competition, though the new host has yet to be confirmed. Britney's fiancé Jason Trawick joined her for the big NYC day, which they wrapped up with dinner at ABC Kitchen later in the evening. While Britney has her new role to look forward to, she also still has a wedding to plan since she and Jason became engaged late last year.