Make swatch background/text reactive to their partner.

[lewisgoddard]

I assume this will require some JavaScript magic to identify when something has too little contrast.

[lewisgoddard]

I'm not sure I can guarantee that this returns >= 0 and <= 255, but otherwise it works.

<?php
////	Get Brightness
// Returns a brightness value from 0 to 255
// for a given 6-digit hexadecimal color string
function get_brightness(string $hex): number {
	// strip off any leading #
	$hex = str_replace('#', '', $hex);
	$c_r = hexdec(substr($hex, 0, 2));
	$c_g = hexdec(substr($hex, 2, 2));
	$c_b = hexdec(substr($hex, 4, 2));
	return ( ($c_r * 299) + ($c_g * 587) + ($c_b * 114) ) / 1000;
}

Constructing an equivalent in JavaScript shouldn't be too difficult.