I had a similar issue on a WordPress site a few months back—added a review carousel to the homepage and no matter what I changed in the settings, the white background just wouldn’t go away completely.
Turned out the carousel was inside a container with its own styling, and I had to tweak the CSS for that parent element too. If anyone else runs into this, try inspecting the section using browser dev tools and see which div is controlling the background.
Also, make sure you’re not just changing the background for the carousel itself, but for the whole section it’s inside. In my case, adding a background-color and making sure padding/margins were set correctly in the customizer fixed it.