function command( repl ) {
	return onCommand;

	/**
	* Returns a list of available syntax highlighting color themes.
	*
	* @private
	* @returns {Array<string>} list of available themes
	*/
	function onCommand() {
		return repl.themes();
	}
}
Returns a callback to be invoked upon calling the `themes` command.

@private
@param {REPL} repl - REPL instance
@returns {Function} callback