Which option changes the background color of the payment box on the checkout page?

I assume you’re asking about a WooCommerce checkout page? If so, the colors and layout for the checkout page are determined by your site’s theme. There isn’t an option to change that color, per se. Rather, you’ll need to override your site’s CSS.

If you can include a link to the checkout page in question, I’ll see if I can provide more specific guidance. But without knowing which theme your site is using, I can’t tell you what specific CSS you’ll need to modify in order to change the background color of the payment box on your checkout page.

I’ll be standing by…