Difficult to think of a true blue flower, other than a few, and Alliums are not on my list. All seem a blue shade of violet, and my camera does not report them faithfully.
I call some Gentians true blue, Forget Me Not, and Heavenly Blue Morning Glory, but not too many more.
Some catalogs are notorious for inaccurate coloring.

bogturtle, the catologs inquestion are American Meadows and Bulbs Direct.