If you work on many different APEX environments, as I do, from APEX 21.2 you can easily set up a banner that will be visible on the left or the top of the APEX Builder to easily identify the environment.
You can do this on instance or workspace level. To modify this on the instance level you need to log in as instance admin (Manage Instance > Define Environment Banner):
On the Workspace level, you can do this in Manage Service > Define Environment Banner.
Unfortunately, API for setting Workspace params currently (APEX 21.2.0) doesn't work:
Tested in APEX 21.2.0