I bought the case of flag blue off the ebay vendor but haven't gotten to point that I'm ready to roll it on my K5. I did a test piece that was white (which is what I'll be rolling over) and it lightened it up but not alot. Flag Blue is a VERY deep, rich blue that at first glance you think is black.

I picked up the interlux book at West Marine and their sample card in there is even darker. As Marq said, the base coat will influence it but only slightly.

Interesting tidbits on what flag blue actually means. I did not know that is the genuine US Flag color blue. That's pretty cool.