You can do this just by adding :
Here you force the main content to be blue instead of white for instance (will work for page/post/projects) but sections have their background set to white by default, so when adding a section, you’ll have to select a color for background or activate “transparent background” to see the color you selected.
Why do section have a default background color… Just because it allows you to mix different colors on a same page i guess.
Hope it’s clear enough
Sent from my Samsung Galaxy smartphone.