At least one way to change tab colors is to use color parameter in Connection Types.

1. Right-click on any connection and click "Edit Connection"

2. Go to General folder on the left

3. There below "Connection name" and "Description" you will see connection type with the button "Edit connection types", go there

4. There, apart from configuration of connection itself, you will be able to change color of the connection itself in the Database Navigator, but at the same time it will change color of the tab which uses this connection.

I believe default Type for all tabs you create is "Development" and you can change it's color, as well as create your custom types with custom colors which I find quite helpful to be able to distinguish various connections and DBs you have. For example ones I've made is for ClickHouse and GreenPlum connections, you can see them on screenshot.

So tabs themselves will look like that