Gems Icon Set is a spinoff of Royal Z and Papirus for Gnome, XFCE and Budgie. At current state their are 4 colors: Citrine, Ruby, Emerald and Sapphire - But more will be added in a near future. Please request your favorite application(s) you think should be in the icon packs.
Github: GitHub - SethStormR/Gems: Gems Icon Set is a spinoff of Royal Z for Gnome, XFCE and Budgie DE.
It uses the Symbolic icon due to it being the 16x16 sidebar. In some icon sets, the symbolic icons are more sparse on the intricate details and clearer; easier to see.
Many applications that need to call on a Clear but tiny button image (Toolbars for example or Menus) will refer to the Symbolic icons.
Titlebuttons fall under this pretty often, too.
In a themes .css, you can change this by setting the -gtk-icon-style: regular; instead of -gtk-icon-style: symbolic;. You can also change this in a specific apps .py file by removing Symbolic - if needed.
Let me think on that a bit ..... got to go back through my saved Themes and find what I lack in Icon Themes .... some are really hard to match colors with .... I like dark themes but not to black like maybe a dark gray something along the Aravisian mercury Theme .... I'll take a look later today and let you know then or maybe tomorrow ....