In libgedit-gtksourceview, a style scheme (or also called color scheme) is used for the syntax highlighting.
A style scheme is defined in an XML file.
See the style scheme file format documentation.
To find style scheme files, libgedit-gtksourceview looks by default at several directories, relying on the XDG Base Directory Specification:
${XDG_DATA_HOME}/libgedit-gtksourceview-300/styles/
${data_dir}/libgedit-gtksourceview-300/styles/
data_dir
of ${XDG_DATA_DIRS}
.On a typical GNU system, this usually includes:
~/.local/share/libgedit-gtksourceview-300/styles/
/usr/local/share/libgedit-gtksourceview-300/styles/
/usr/share/libgedit-gtksourceview-300/styles/
The libgedit-gtksourceview team prefers to just keep a small number of style schemes distributed with the library. To add a new style scheme in libgedit-gtksourceview itself, the style scheme must be very popular, and ideally a libgedit-gtksourceview-based application must use it by default.