What does it do?

It's for playing with colours.

You can convert colours from one format to any of the other formats, for example:

<?php
echo Hex::create(0xCC0000)->toCMYK();
echo Hex::create(0xCC0000)->toCIELab();
echo Hex::create(0xCC0000)->toCIELCh();
echo Hex::create(0xCC0000)->toRGB();
echo Hex::fromString('black')->toHSV();
echo RGB::create(200,100,150)->toHex();
?>

Or find colour harmonies, modify colours or match colours:

<?php
echo Hex::fromString('#cc0000')->greyscale();

echo Hex::fromString('#cc0000')->websafe();

echo Hex::fromString('#cc0000')->match(array(
  new RGB(0,0,0),
  new XYZ(1,1,1),
  new Hex(0x00FF00)
));

echo Hex::create(0xFF0000)->range(Hex::create(0x0000FF), 100);

echo new RGB(100,0,100)->split(2);

echo new RGB(100,0,100)->hue(-2);
?>

I should document it properly at some point with examples.

(no syntax highlighting? :()

Edit: oh, I kinda have a bit. https://github.com/mikeemoo/ColorJizz-PHP/

So did he.

Uhrmm... :/