Yes, the dark hard canna seed is the mature seed.

Thanks jenna1. I had read some posts where they said to toss the tan seeds but when I noticed this morning, the tan seeds turned dark brown/black, I was amazed that they seemed to be maturing even though they had not been when I opened the seed pod. I was not sure if this was typical with canna seeds that they would continue to mature, ie turn that dark brown/black color, even though they were not 'black' when the pod was opened. I'm bagging and marking these a questionable to germinate for next year.
Good to know I don't have to toss these.
Our first frost has not hit here yet so the cannas are still opening new flowers. I'll be digging the rhizomes out of the pots shortly after the stalks die off and save them for next year. Lots of seed pods to harvest as well.
Thanks also for the email on planting the seeds. I'll see what happens next year when I try to grow from seed and see which ones actually grow.

Julia