Hi Tom,
You can achieve what you need, by setting the values of some CSS variables on the root section of tyour Theme:
:root {
/* App Settings */
--header-color: #ffffff;
--footer-color: #ffffff;
--color-background-body: #ffffff;
}
If the above example, the background color will be white, for Header, Content and Footer (change '#ffffff' to your desired color).
Hope this helps.
Best regards,
Paulo