The main reason for painting a catalytic converter is theft deterrence.

I spent the past couple of weeks researching (googling) how to paint a catalytic converter and spent this weekend actually painting the catalytic converter on my recently purchased SUV. I documented my experience and put it in a PDF (5 pages) that I am happy to share. It's not difficult but there are things that may be helpful to know before starting. I intend it a guide and idea source, but not as a last word on painting catalytic converters.

PM an email and I'm happy to send the PDF.