Thanks again for sharing and glad to see your success.
The finish looks great. I expect it will work out well for you.
As to color, there are many versions of acetal (POM) available for molding. I don't know what is commonly sold in "stock" shapes.
The colors often follow the fillers, and the fillers are used to modify for specific properties. Black could be a graphite-filled version, which would be marketed for bearing applications.
Way back, we would use blends with PTFE fillers for machine bushings. I recall spec'ing "Delrin AF" but that was when DuPont probably owned the market. Yes, I'm a dinosaur.
Here's a good description of the material and why it is a "workhorse" for product designers. I think the list of different grades is interesting:
https://omnexus.specialchem.com/sele...ne-pom-plastic