PHP generate RGB

Use a cryptographic hash and clip the bytes you don't need:

function getColor($num) {    $hash = md5('color' . $num); // modify 'color' to get a different palette    return array(        hexdec(substr($hash, 0, 2)), // r        hexdec(substr($hash, 2, 2)), // g        hexdec(substr($hash, 4, 2))); //b}

The resulting (code to generate it) looks like this for the numbers 0-20:

<?php // someting like this?$randomString = md5($your_id_here); // like "d73a6ef90dc6a ..."$r = substr($randomString,0,2); //1. and 2.$g = substr($randomString,2,2); //3. and 4.$b = substr($randomString,4,2); //5. and 6.?><style>#topbar { border-bottom:4px solid #<?php echo $r.$g.$b;  ?>; }</style>

The obvious approach is to just convert the ID into a color (e.g. lower 8 bits are the blue, next 8 bits are Green, next 8 are Red - leave 8 bits, but I'm sure you can figure that out ;-)

Assuming this doesn't work (cos you end up with a horrible color palette:Use an array (or hash table) to make a mapping of IDs to Colors.

If you are concerned that there are too many IDs, then you could apply some hash to the ID and use that as you key into the "id to color" mapping. In this case you are effectively saying one id always has one color, but one color can be used by many IDs.