After searching online iris descriptions, I found a match - these were Invitation. I shared my discovery with the friends, who informed my that they were happy to have given them away - bi color iris are not their favorites.
The Invitation iris are tall and have the largest blossom heads of any iris in the yard. Consequently, they fell over after the slightest rain, and needed to be placed on crutches. They also multiplied very easily after planting last summer, so dividing will probably be needed this year. I believe our fall plant swap already has some material.
For The Record:
Dry clay soil
Bone meal fertilizer in the fall with gypsum for the clay soil
Blooming: allium, purple salvia, dutch iris
Tomato seedlings planted, nasturtium seeds planted