This is something that needs a design decision on. Looking at the Figma doc, I don't see a mobile design as of now.
What I did in the PR was use the same background as is used on desktop. In previous versions, this was a solid color instead. If we want to do that instead, just let me know what color. I think this is the better bet so the text doesn't conflict with any of the colors of the header.
You can preview this by applying the patch from https://github.com/WordPress/wordpress-develop/pull/5534 to your local. I've also shared a screenshot above of the Get Involved page to demonstrate the conflicting that I think should be avoided.