Images is alllll black in the thumbnails window where as i wish it to be white

please see attached crows jpg

looking at the jpg you see the infill area between the images is alllll black in the thumbnails window where as i wish it to be white. i cant figure out how to change the colour to my choice: white

if i double click the image (crows) it opens in the viewer pane and has a white background which is what i want

with thanks

It must've already been changed, as it would not be black by default in light mode.

Preferences / Colors and Fonts / Directory Opus Colors / File display background.

That can also be overridden for individual folders or types of folders via Preferences / Folders / Folder Images.