Well, basically a shared library built as part of the primary build of LibreCAD should be present.
For Windows, there should be <LibreCAD_INSTALL_DIR>\iconengines\lc_svgicons.dll.
If one is present, using the Widget options dialog, it is possible to customize values of three base colors present in icons.
I've noted that in my pull request there -
https://github.com/LibreCAD/LibreCAD/pull/2078and here is a link to the demo video.
BTW—external icons that are located in some given directory are also supported (the name of .svg icon file should be the same as used internally).
However, it might be that the shared library file itself is not included in the installer package - have to check this.
p.s—usually, I note the information about new and changed features in my pull requests. However, it might be that they are closed too fast and so are not visible to the majority of users.
Just in case, more details about various changes can be found there:
https://github.com/LibreCAD/LibreCAD/pulls?q=is%3Apr+author%3Asand1024+is%3Aclosed