Shoot them an email or give them a call and they should do it for ya no problem and then send you a quote for the total.
If you want blue color, add some Pentosin G11, which Petras also sells. It will give your water a lightish blue color.
If you want something more than that, take a look at the Primochill and/or Feser tubing which comes in several colors.
The reason you really don't want to use any dyes or whatnot is because they often will come out of solution and clog up bits like the radiator and cpu block.