The answer to this question can be found in the first chapter of this excellent novel. We are told that Winston Smith, like other party members, all wear the same uniform which consists of blue overalls. What is significant about this uniform, as is the case with any form of uniform, that it visibly sets party members aside from other groups in society, such as the Proles, because they are readily recognisable and identified as being Party members rather than anything else. In addition, you might like to think about the way in which having one uniform for all party members suppresses their own personal identity and ensures that the bigger identity of the Party is the dominant identity that defines who they are. We are presented with a totalitarian world where those who live in it are given little if any freedom of choice, and the uniform servers to underscore this bleak reality.