I have not tumbled the one brass I tested the green nail polish on but will probably do the same treatment to a few more and then throw them in the tumbler with the next batch just to see. I suspect it will hold up decent but we'll see.
The blue color I ended up going with was actually a permanent poster marker from the drug store. A friend gave me the tip on them as they worked good for him. I'm sure it will come off in the tumbler, or at least come off enough to need doing again, but it really didn't take much time at all.
I'm still tossing around the idea of making a jig to hold 20 or so shells just right so I can Cerakote the heads pink or something but we'll see. This marker method is so simple, fast, easy, and cheap which are all great reasons to stick with it assuming it works out decent.
When you do tumble, please let us know how it held up. I'm thinking of doing the green trick to help me ID number of times reloaded and maybe just put a dot of colored polish for each time reloaded. What type of media is in your tumbler?