Board Thread:Support Requests - Designing Your Wiki/@comment-33601278-20201008145002/@comment-9605025-20201008224434

In order to change the color of each header individually, you will need to use header tags directly instead of the wikitext markup. When using headers this way, you can change the background color using inline CSS.

That said, it sounds more like you want to change it for specific pages. In that case, see this page on creating page-specific site CSS. If you are unfamiliar with site CSS, I can explain further.