Hi Elaine and thanks for your questions and pictures of your Ironwood tree. I was not familiar with this species, so it was intriguing to figure out why the leaves had that purple color.

 It turns out that the tree does not tolerate wet soils, and I see a lot of moss around the base of the tree, indicating lots of water there. This may have stressed the tree some, so that it got a fungus on some of the leaves. I would pick off the purple ones and destroy them (in the garbage, not compost) so the fungus doesn't spread. This may take several pickings this fall.

Then make sure the tree doesn't get so much water. Of course, you can't control the rain, but let it dry out as much as possible and water it infrequently over the summer. This tree is supposed to be pretty drought tolerant which is a great thing for our new climate summers.

I hope this helps and you have time to pick off the leaves.