Hi Jack - I see your post history includes some manual CSS overrides for background colors. I’d be interested to see the site, but it sounds like you might be trying to work around an override to the site header section that’s unexpected by Discourse themes. Typical dark & light palettes play nicely with light & dark logos on the signup page…
…but if I’d been counting on always using a white logo I’d have the same problem.
Does this sound like what you’re encountering?