There are two ways that can be used to change the Guidethrough Launcher background colour.
1. Using a specific hex colour code
The process to change the the Launcher background colour using a hex code is explained in this video.
If you don't know what hex code to use, or if you only have the RGB code, then this site can be helpful: https://htmlcolorcodes.com/
Whenever the Launcher is changed, you will see the preview of what the Launcher will now look like in the centre of your screen.
2. Using the embedded colour picker
The process to change the the Launcher background colour using the embedded colour picker is explained in this video.
Whenever the Launcher is changed, you will see the preview of what the Launcher will now look like in the centre of your screen.