+
+Similarly to how the glyph's image specifier works @xref{Creating
+Glyphs}, you don't create your own image specifier, but rather add
+specifications to the existing one. Note that the image instance that is
+generated in order to actually display the background pixmap is of type
+@code{mono-pixmap}, meaning that it's a two-color image and the
+foreground and background of the image get filled in with the
+corresponding colors from the face. (#### Is this still true?)