Use the function 'TagColour' to create a 6 character hex code for a colour that isn't too bright (ie, shows up against white) for any input string. Or, supply an existing colour name (red, blue, green etc) and get it back as a usable code.

gistfile1.php[345]

<?php
	function TagColour($name){
		$colours = array('red', 'blue', 'green', 'black', 'brown', 'cyan', 'gold', 'yellow', 'grey', 'gray', 'indigo', 'lime', 'navy', 'yellow', 'orange');
                if(in_array(strtolower($name), $colours)){
                        return strtolower($name);
                }
                $hex = substr(md5($name), 1, 6);
                $intensity = (HexIntensity($hex) / 255) * 100;
                $i=0;
                while(($intensity > 70) && ($i<10)){
                        $hex = IntensifyHex($hex);
                        $intensity = (HexIntensity($hex) / 255) * 100;
                        $i++;
                }

                return $hex;
        }
	
	function HexIntensity($hex){ //strlen = 6
	        $colours = HexToRGB($hex);
        	$brightness = (($colours['r'] * 299) + ($colours['g'] * 587) + ($colours['b'] * 114)) / 1000;
        	return $brightness;
	}

	function IntensifyHex($hex){
        	$c = HexToRGB($hex);
	        $r = $c['r'];
        	$g = $c['g'];
  	      	$b = $c['b'];
        	$min = min($r, $g, $b);
        	$max = max($r, $g, $b);
        	if($r == $max){
        	        $r = $r * 0.6;
        	} elseif($g == $max){
        	        $g = $r * 0.6;
        	} elseif($b == $max){
        	        $b = $b * 0.6;
        	}
        	return RGBToHex($r, $g, $b);
	}

	function HexToRGB($hex){
        	$hex = str_replace("#", '', $hex);
	        $colour = array();
        	$colour['r'] = hexdec(substr($hex, 0, 2));
        	$colour['g'] = hexdec(substr($hex, 2, 2));
        	$colour['b'] = hexdec(substr($hex, 4, 2));
        	return $colour;
	}

	function RGBToHex($r, $g, $b){
 	       	$hex = '';
        	$rh = dechex($r);
        	$hex .= (strlen($rh)==1) ? $rh.$rh : $rh;
        	$rg = dechex($g);
        	$hex.= (strlen($rg)==1) ? $rg.$rg : $rg;
        	$rb = dechex($b);
        	$hex.= (strlen($rb)==1) ? $rb.$rb : $rb;
        	return substr($hex, 0, 6);
	}

?>