In T4214#99869, @epriestley wrote:

Ah, right, we're using the immutable cache, which is DB-backed. You should be able to clear it with:

$ bin/cache purge --purge-all

We should also probably put the PHID in the cache key.

I was easily able to get it to display a logo image that I uploaded to the files app. However, I didnt like the result. I followed the same process to configure an alternate image but it doesn't work. It accepts the setting and saves the correct PHID, but when the page is rendered, the inline css still points to the old image. It's not related to caching because I cleared my browser cache and I also cleared php cache and restarted nginx. If I remove the custom logo from the config, it goes back to default. Though when I add any other PHID to be the logo it displays nothing at all in the logo area (b/c the image it tries to show doesn't exist).

Obviously its configurable. The message on the config page said to let you know if there was a protocol that should be considered for inclusion by default.