Hello,
I saw the screenshot you attached. To remove the background overlay color from the categories grid you need to add the following Custom CSS in the Global Custom CSS area under Theme Settings >> Custom CSS.
.cat-design-center .wrapp-category::before {
background: transparent;
}
You need to change the color of the more products text as well because when you remove the overlay they will not be visible. So you need to add the following CSS to change the color.
.cat-design-center .more-products {
color: green;
}
You can set the color according to your needs.
Best Regards.