I use PL/SQL Developer to connect to test databases and production databases. I have used other tools that give you a way to make it clear when you are in production. For example, some tools allow you to make the SQL window's tab red when you are connected to a production database. Does PL/SQL Developer have any way to configure a connection to mark the SQL Window as production in some way? Any way to display production connections in bold or red or something like that?

In connection screen, you have a check box : indicator color.

You can see too, in Preferences \ Appearence \ Connection indicators

You can also use the Connection Indicator settings in the Appearance section of the User Interface settings to set connection colours depending on the database (or individual user) you are connecting to