The present invention relates to a process of preparing a polycondensate in the presence of a fluorescent whitening agent and at least one phosphonate and/or phosphinate. Further aspects of the invention are a polyester prepared according to this process and composition comprising a polycondensate, a fluorescent whitening agent and at least one phosphonate and/or phosphinate. Yet another aspect is the use of a fluorescent whitening agent and at least one phosphonate and/or phosphinate for improving the color of a polycondensate.