How to edit the font color of the H1 on a single page?

If you’re using body_class and post_class correctly, you should have CSS classes you can match against that take the form postid-0001 etc

Next you need the CSS to change the h1 colour

Find the ID of your membership page, and use the CSS class in your CSS selector so it only matches on that page.

e.g. .postid-0001 h1 { color: red; }

Ofcourse your membership title may not be a h1 element, and at this point it’s a pure CSS question. Use the customizer to put your CSS code in and hey presto, your title colour has changed