Looks to me as if it's up to the user to assign them to specific clips, for convenience. And the choice made seems to tag the specific clip.
Loaded a singer/music file and changed it to purple.
Restarted, loaded it again - purple.
Restarted and loaded another singer/music - green.
Reloaded the prior purple file and overlaid it - still purple...
Yet this wasn't 100% true. On some tests it had turned green. But colorful.😄