detect hex color is dark or light and return css class to use in to invert colors

is_light_color.php

<?php
function prefix_hex_is_light( $color ) {
	if ( ! $color ) {
		return false;
	}
	$hex = str_replace( '#', '', $color );
	$c_r = hexdec( substr( $hex, 0, 2 ) );
	$c_g = hexdec( substr( $hex, 2, 2 ) );
	$c_b = hexdec( substr( $hex, 4, 2 ) );

	$brightness = ( ( $c_r * 299 ) + ( $c_g * 587 ) + ( $c_b * 114 ) ) / 1000;

	if ( $brightness < 128 ) {
		return 'lighting-colors';//the color is dark
	} else {
		return 'darking-colors';//the color is light
	}
}