PAP bluing solution is a variant of Scott's solution and is used specifically in Papanicolaou staining (Pap staining) for cytological smears. It is used to bluish the hematoxylin in the stained nuclei to improve contrast and visibility, which facilitates the interpretation and analysis of cytology specimens.

Instead of the rinsing step in tap water, PAP bluing solution is used to obtain more reproducible and consistent results. The solution is an important component of Pap staining and helps increase the accuracy and reproducibility of cytological staining.