Johan, I have three of Dan's that show blue in his pictures. The first is Debra Jorgensen, but here are the other two. I'm posting Dan's pictures because mine really do not show the bluish color that his pictures do, and that's probably because of our lack of humidity and our early summer heat.
SHARPLY FOCUSED
TESSA ANN - When Paul Lewis posted his garden video through his blog a couple of years ago, he indicated that he thought TESSA ANN was the bluest daylily to date.
Another one that I am very fond of, although it is by Guy Pierce at Floyd Cove Nursery, is OCEAN LOTUS.