Ventura wallpaper slideshow background color

Hi, I upgraded to Ventura recently, and I had a rotating photo slideshow as my wallpaper. I changed it tonight to a different folder of photos, but the background color, behind/around the photos if they're not full-screen-sized, is one that doesn't match the new set of photos. On previous macOSs, I knew how to change the background color, but I can't figure out how to do that with a photo slideshow in Ventura. How do I change the background color behind the rotating photos?

Thanks!