The bleeding? Polypaint is vertex painting. The vertices on the borders of 2 groups are sharing 2 colours. Polypainting requires a dense topology to get a crisp edge.
This is an older article (PlayStation 2!) but the pics and text are great, worth a read. https://www.gamasutra.com/view/feature/2987/tool_postmortem_climax_brightons_.php?page=2