Try https://b.piefed.social/ instead! Log in with the same username and password as piefed.social.
It works best on a phone / tablet but on a desktop it’s fine too once you switch to compact mode.
It can be installed as a PWA.
There are also lots of themes you can try at https://piefed.social/user/settings. Here are some screenshots of them - https://join.piefed.social/screenshots/
The Amethyst theme in your user settings is mostly a recolored version of the default theme that is pretty popular. You could give that a shot. The HPT themes are a bit more of a departure, but they have lots of fans out there as well.
The colors are all overwrite-able via custom css in your settings if one of those options doesn’t work. Which elements are you looking to recolor? We use Bootstrap css for the web ui, so you would just need to overwrite the default colors that Bootstrap uses.