On this answer, status-review is mentioned. For whatever reason, the tag appeared as blue instead of red. I've also noticed that it does not appear on this post for some reason. I thought that editing the post after the tag became moderator-only might turn it back to red, which is why I proposed a minor edit to the post. Sure enough, it changed to red when it was approved, but inactive posts that aren't edited could keep the blue tag indefinitely.
This is because posts are stored as HTML. At the time the answer was submitted the build wasn't live. Therefor the tag wasn't a mod-only tag yet. It got no special handling. An edit will re-render the HTML and store a new version of the HTML. As the tag has now become mod-only it will render as red.