Hi @olympesmn
If you need it on all pages, you don’t need to add the ACF field to a Gutenberg block.
So add the ACF field and under rules, set the post type to page (assuming it’s pages you need it on).
In your code, you then call the field like a normal ACF field
So something like:
<div style="background-color:<?php the_field('background_color'); ?>">
</div>
