If you dislike the new default colors, just go to theme settings and select "photon classic"
This new update allows instance admins to set their own themes (via PUBLIC_THEME) and allows you to have multiple theme presets.
It's available on phtn.app right now, coming soon to a release
That was added in a random update, (i will often push new updates to phtn.app that aren't a part of specific releases, because phtn.app always has the latest updates, even if i haven't released them as a tag yet)
It also uses your accent color now :)