If you wish to modify the standard colour set built into
ls, you need your personal copy in your home directory, which you get with
cd ; dircolors -p > .coloursrc
After modifying this well-commented file you need to have it read into the environment string LS_COLORS, which is usually done with
eval `dircolors .colourrc`
You need to put this line in your .bashrc/.cshrc/.tcshrc (depending on your shell), to have it done at each login. See the dircolors(1) manual page for details.