Hey Hordecall, first of all thanks for your donation! About your problem, I assume you've already tried changing the base color of the theme? This also affects the tile palette background somewhat (if you're on macOS, change to "Tiled Fusion" theme first). Another option is to try a development build where I've coded a background color option per-tileset, though unfortunately it's a little unstable at the moment. You can find the latest build for Windows here.