Hi!! So:
- If you want to change the background color in Kustom just open the editor, go to the Background Tab and change the settings there (set background to solid color and change the color)
- If the color has a "globe" icon on its right then it means that its a Global so you cannot change it from there but you need to go to the "Globals" Tab and change it. When you change a Global you will also change all the items that are mapped to that specific global
- In general on complex themes the designers exported most of the configurable options in the "Globals" tab so its usually better to check that first, if you want to "unlink" a property from a Global just select it and press the Globe icon again on top so you can change it separately
Hope it helps!