function colorDarkness ( $col )
        {
#-k     color
#-      given  a hex color, what is its relative darkness?
#-p     $col    - req   - Hex RGB color (Must be in the form #hhhhhh)
#-p             - ret   - Array 0..4 entries of different interpretations of darkness, each (float) 0..1; 0 is white up to 1 black
#-c     credit: http://stackoverflow.com/questions/1855884/determine-font-color-based-on-background-color
#-c     credit#3: http://stackoverflow.com/questions/596216/formula-to-determine-brightness-of-rgb-color
#-d     2/18/21 Fixed

        $r = 255 - hexdec ( substr($col,1,2) );
        $g = 255 - hexdec ( substr($col,3,2) );
        $b = 255 - hexdec ( substr($col,5,2) );

        $ar[0] = (0.2126*$r + 0.7152*$g + 0.0722*$b)/255;               #       Luminance (standard, objective)
        $ar[1] = ( 0.299*$r +  0.587*$g +  0.114*$b)/255;               #       Luminance (perceived approach 1)
        $ar[2] = sqrt( 0.241*$r*$r + 0.691*$g*$g + 0.068*$b*$b )/255;   #       Luminance (perceived approach 3)
        $ar[3] = sqrt( 0.299*$r*$r + 0.587*$g*$g + 0.114*$b*$b )/255;   #       Luminance (perceived approach 3)
        if      (($r>128)&&($g>128)&&($b>128)) $m = 1.0;        # def light
        elseif  (($r<128)&&($g<128)&&($b<128)) $m = 0.5;        # def dark
        $ar[4] = $ar[3]*(1+$m)/2;
        $ar[4] = 1-colorRelativeLuminance($col);

        return  $ar;
        }

?>