How to change background color in slideshow mode?

Hello, In the slideshow mode I am trying to either delete the muted images that are behind the main slide OR change the color completely. In the screen grab you can see the muted background.

Thank you!

You mean overlay background behind image? If you share link to this page, we can give some lines of code to fix it

You can use this code to Website Tools > Custom CSS

/* Lightbox Mode background */
div.gallery-lightbox-background {
    background-color: #000 !important;
    opacity: 0.9 !important;
}