I have been painting the inside that military flat olive green it's a Testors brand. It looks close to the money when done.I like those blanks and have made a few pens with them. I'm still undecided on the best color to paint the insides with though, I've tried light silver-green and darker metallic green and each was OK but not awesome. letting the brass tube show through wasn't so bad on another where I left the body a little thicker. They offer a lot of flexibility, that's for sure!