Hi @Ifym, welcome to our forum!
Do I understand correctly that you want to change the background colour of your homescreens, or is there somewhere else you want to adjust the colour for the background?
If you go to your home screen (tap the middle icon at the bottom of the device) > press and hold on an empty area of the display > tap "Wallpapers" and you have some different ones to choose from. Here you can also use a photo or a saved picture and have that as your background.
You can also tap on "Themes" instead and have a look what is available there. If you don't find any that you like, you can tap on "Get more themes" and see what is available.
I hope that helps! 
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