dye's are a BIG NONO - as mentioned by bigcyco,muffin+rockdpm. If you want color in your loop, get colored tubing. There's a thread on the net on how to color/dye your own tubings...and how much color you'd want them to be. Though it means wrecking the kitchen and ruining a pan for boiling the tubing and dye in.
Dye's break apart over time and the other thing about dye's is that they stain in order to give off the color, thus the high restriction of choices on some parts such as tubed res' and some blocks. BTW the blocks also get stained, ever wonder how people don't show cleaning/block tear-apart pics?
Dye's raise the temps of a normal efficient loop by about 4C sometimes upto 8C but by this understand that dye's are mean't for a show...not full time usage.
*check out the watercooling build log thread and/or the watercooling gallery thread - there's a rig of a green+black themed build. maybe thas the color you'd want, should be a PM away for some advice.