''My favorite color at the moment is pink,'' says Oscar's youngest Best Actress nominee, Keisha Castle-Hughes. The 13-year-old ''Whale Rider'' star has chosen designer (and fellow New Zealander) Liz Mitchell, who says the frock will likely reflect her client's Maori heritage. Whether or not Castle-Hughes is in the pink come Feb. 29, the teen might find herself turning the shade: Her $12,000 goody bag from Victoria's Secret (given to all Best Actress nominees) will include a racy bra-and-panties set. Counters a VS rep: ''The bra we chose isn't so sexy that a young girl would be ashamed to wear it.'' Plus, it's pink.