Well, I have Cool Blues on my car right now; the difference between stock is brighter, but not as bright as the silverstars. It's somewhere in between - just like what Sylvania described it as. Also, it has a slight bluish tint, not as blue as those ricer/xenon/plasma 80w bulbs however.
Paired up with an upgraded harness, the change from stock is pretty significant. I was really amazed at how much changing the harness brought out the full potential of these lights.