There are hundreds if not thousands of plain blue iris. The simple shape makes me think your looking for an old historic. Try HIPS. Maybe one of the pictures will ring a bell.
Also njiris and LaurieF and garden of Mu have pages with lots of historics.

Perhaps Iris pallida

Here is a link that might be useful: Iris pallida

I second i. pallida. It's a wonderful iris - great scent and it takes quite a bit of shade and still blooms here. Great Lakes is a nice old light blue, and Missouri a good medium blue. Both are Dykes Medal winners and easily found in commerce. All lean to the lavender side though. The blues get truer as you get more modern, but then more ruffles show up. They can appear more blue if planted with purples from the red-violet side.

Mike

My fave blue iris is called "Eleanor's Pride" - it's fairly ruffled but it is a true light blue, like forget-me-nots.

As I remember it, it was almost like the form of I. albicans, without the rolled edge of the falls (maybe that was just on that one picture), and it was a medium blue. This website has a photo that looks somewhat like it, but I remember that it was more of a solid color withouth the various blues:
http://www.badbear.com/signa/display-photo.pl?Iris-albicans+4+3

Anyone have anymore guesses as to what I saw in Minneapolis?

LisaBC~

does anyone know where i can purchase I. pallida? I need approximately a couple hundred of them.

thanx

Great Lakes is a common medium blue. Here's a nice picture of it. It's an older one also.

Here is a link that might be useful: Great Lakes