The white exterior and spartan grey staircase of Jian Yang's tidy house gives no hint of the shock that lies within: a pink living room floor and his collection of more than 6,000 Barbie dolls. The 33-year-old Singaporean favors minimalist decor, but the Barbies — and 3,000 dolls of other kinds — dominate three sides of the main room and spill over to fill nine mirrored cabinets in his dressing room and the shelves of his study.