You need  Root rights for /usr/share
so just open Nautilus in a Termina with root / "sudo nautilus" / and copy then 

Just copy ngc.lang.txt file to either (REMOVE THE .txt EXTENSION)
/usr/share/gtksourceview-3.0/language-specs/
or
~/.local/share/gtksourceview-3.0/language-specs/ (you can also use 2.0 instead)


and GCode.xml (colors) in
/usr/share/gtksourceview-3.0/styles/
or
~/.local/share/gtksourceview-3.0/styles/
then restart gedit, open a ngc file and select GCode color scheme



