For the Galaxy Rollup at EGD I made a background image of a galaxy in Galaxys colors. If you want to use this image for any promotional material, we uploaded it from 3 angles in different resolutions, and I wrote a guide on how to customize it here:
it would not be all that hard a job.
I think you're right regarding our members, but the other side of that is that some servers will defederate from you, if you're not defederating quickly from the "wrong" instances (nazis, free speech types, etc.) and that just seems like a headache to keep up with the drama.
(or if you prefer meme form)
I'd just like to interject for a moment. What you're referring to as Mastodon, is in fact ActivityPub/Mastodon, or as I've recently taken to calling it, ActivityPub plus the Mastodon API