Specify -symbolic suffix
Both GNOME and KDE append -symbolic
to the ends of some or all icon names, but for different purposes.
In GNOME, it's a hint to the GNOME icon loader implementation that means "please re-color this icon as needed when using a dark theme".
In KDE, it uses the existing icon lookup fallback logic (as well as clever use of symlinks in the Breeze icon theme) to return the calling app a symbolic icon (if present) when otherwise a full-color one would be returned.
The GNOME approach is an implementation detail of how re-coloring is done there (see #24), so I'm not sure it's suitable for specification. I won't claim that the KDE approach is optimal, but in principle I like it better since it's backwards compatible and gives app developers something they didn't have before: control over what kind of icon their app gets (symbolic or full-color) when using an icon theme that has both types for a single icon name as Breeze does.
I don't know if any other FDO icon theme users do the -symbolic
thing, but would be interested in hearing from them if they do regarding what they use it for.