color_tests.php

<?php

/**
* Convert RGB colors array into HSL array
*
* @param array $ RGB colors set
* @return array HSL set
*/
function rgb_to_hsl($color){
    list($r, $g, $b) = is_array($color) ? $color : hex_to_rgb($color);
    $round_to = 1;
    
    $clrR = $r;
    $clrG = $g;
    $clrB = $b;
    
    $clrMin = min($clrR, $clrG, $clrB);
    $clrMax = max($clrR, $clrG, $clrB);
    $deltaMax = $clrMax - $clrMin;
    
    $L = ($clrMax + $clrMin) / 510;
    
    if (0 == $deltaMax){
        $H = 0;
        $S = 0;
    }
    else{
        if (0.5 > $L){
            $S = $deltaMax / ($clrMax + $clrMin);
        }
        else{
            $S = $deltaMax / (510 - $clrMax - $clrMin);
        }

        if ($clrMax == $clrR) {
            $H = ($clrG - $clrB) / (6.0 * $deltaMax);
        }
        else if ($clrMax == $clrG) {
            $H = 1/3 + ($clrB - $clrR) / (6.0 * $deltaMax);
        }
        else {
            $H = 2 / 3 + ($clrR - $clrG) / (6.0 * $deltaMax);
        }

        if (0 > $H) $H += 1;
        if (1 < $H) $H -= 1;
        
        $H = round($H * 360, $round_to);
        $S = round($S * 100 . '%', $round_to);
        $L = round($L * 100 . '%', $round_to);
    }
    return array($H, $S, $L);
}

function hex_to_rgb($hex) {
    $hex = str_replace('#', '', $hex);
    $hex = (strlen($hex) == 3) ? $hex[0] . $hex[0] . $hex[1] . $hex[1] . $hex[2] . $hex[2] : substr(str_pad($hex, 6, '0', STR_PAD_LEFT), 0, 6);
    // bitwise conversion
    $colorval = hexdec($hex);
    $r = 0xFF & $colorval >> 0x10;
    $g = 0xFF & $colorval >> 0x8;
    $b = 0xFF & $colorval;
    
    return array($r, $g, $b);
}
    
    
    
    list($h, $s, $l) = rgb_to_hsl('#CC2801');
    // Alpha transparency (0-1)
    $a = .75;
    
    echo "Hue: $h" . '<br />';
    echo "Saturation: $s" . '<br />';
    echo "Lightness: $l" . '<br />';
    
    echo '<div style="width:40px; height:2em; border:1px solid #000; background-color:hsl('."{$h}, {$s}%, {$l}%".')"></div>';
    $l += 10;
    echo '<div style="width:40px; height:2em; border:1px solid #000; background-color:hsla('."{$h}, {$s}%, {$l}%, $a".')"></div>';

Converts a string in to RGB color profiles.
No additional work has been done to verify contrast, brightness, hue, etc...

// 32-char options: md2, md4, md5, ripemd128,
// tiger128,3, tiger128,4, haval128,3, haval128,4, haval128,5
$fullhash = hash('ripemd128', $string);
$colors = str_split($fullhash, 8); // values for R, G, B, A
foreach ($colors as $i => $hash) {
    $colors[$i] = dechex(bcmod(hexdec($hash), 255));
}

list($r, $g, $b, $a) = $colors;
return array($r . $g . $b, $a);