Make sure that your $TERM is set correctly before running Emacs.

If launching direct from the terminal, check with echo $TERM - preferably its value would be xterm-256color

Set it either directly before you run Emacs:

TERM=xterm-256color emacs -nw 

With any other arguments you need.

As a more permanent solution, set $TERM in your shell profile, e.g. .bashrc or .zshenv (depending on your shell)

export TERM=xterm-256color

If you are running Emacs in a GNU Screen session, use screen-256color as the value of $TERM instead.

Make sure that your $TERM is set correctly before running Emacs.

If launching direct from the terminal, check with echo $TERM - preferably its value would be xterm-256color

Set it either directly before you run Emacs:

TERM=xterm-256color emacs -nw 

With any other arguments you need.

As a more permanent solution, set the value of TERM in your terminal emulator setup.