You may not like the current background colour, or maybe you like to change it to match an exact colour.
In this case you need the colour setters.
Type BS or bs to Show the colour setters.
Type BH or bh to Hide the colour setters.
If you do not move any setter at all, or a few seconds after your last change, the colour setters auto-hide.
To exactly match a known RGB colour you can open the console while operating the colour setters.
Right click and select Setting and then Console from the context menu.
The RGB values are displayed on the console. Make sure you zoom in on the setters to achieve maximum accuracy.