The /etc/DIR_COLORS file is just for reference to the default system colors. Modification to the list of colors must be done on a per-user basis, as stated by the comments at the beginning of the file itself:
# Configuration file for the color ls utility
# This file goes in the /etc directory, and must be world readable.
# You can copy this file to .dir_colors in your $HOME directory to override
# the system defaults.
So you can simply copy /etc/DIR_COLORS to $HOME/.dir_colors and edit your local copy. After that the applied changes should be visible (and for you as a user only). Be sure to exit from the shell where you've applied the changes, that is changes are applied to newly started shell sessions.