function onCommand() {
		var theme;
		var name;

		// If no theme name given, get the current theme...
		if ( arguments.length === 0 ) {
			name = repl.settings( 'theme' );
		} else {
			name = arguments[ 0 ];
		}
		try {
			theme = repl.getTheme( name );
		} catch ( err ) {
			repl._ostream.write( format( 'Error: %s\n', err.message ) );
			return;
		}
		return theme;
	}
Returns a syntax highlighting color theme.

@private
@param {string} [name] - theme name
@returns {(Object|void)} theme object