Let the seed head ripen on the plant. When it splits and you can see black seeds inside, spead them out and let them dry. Then bung them in the freezer for a couple of months. Thaw out and soak the seeds in water then plant in pots. Not many will come up straight away, but when you have enough plants throw the rest in an unused part of the garden as they will germinate later, even 10 years later. You could get some interesting colours if you have plenty of other coloured irises about. But they could just revert to type.
The good thing is if you do have a very interesting one, you can divide and sell, even name it (not officially) but nice to name them after family members for unusual pressies.