User-centric identity management approaches have received significant attention for managing private and critical identity attributes from the user's perspective. User-centric identity management allows users to control their own digital identities. Users are allowed to select their credentials when responding to an authentication or attribute requester and it gives users more rights and responsibility over their identity information. However, current user-centric approaches mainly focus on interoperable architectures between existing identity management systems and privacy issues have not been considered in depth. In this paper, we propose a category-based privacy preference approach to enhance the privacy of user-centric identity management systems. In addition, we present our proof-of-concept prototype of our approach in the Identity Metasystem.