Hi Emile. Thanks for looking.
It seems to be a conflict with a themes colors.php and CoBlocks 2.12.0. Specifically the color pallete used by the theme used to style content in the block editor. My theme is Turnkey Storefront. So my primary color is #009ee2, and it won’t apply that color in the accordion item title background. But if I change the code in the accordion block editor to #009ee3, it works.
I get the same behaviour if I change theme to Twenty Twenty-One. The theme color pallete used to style the block editor is conflicting with the Accordion block editor background color selection and won’t apply. I just get the transparent background, unless I specify a color that isn’t in the themes colors.php.
I’ve deactivated all plugins except CoBlocks and removed all custom CSS. It’s basically back to stock with Twenty Twenty-One theme. And my database is good.
I’m happy to style with custom CSS, but hopefully the above is helpful if it turns out to be a common problem.