Q.Calla lily flowers turning green
When I bought my calla lilies and planted them, the flowers were a bright, beautiful yellow, and stayed that way through most of the summer. Then in early August, when more blooms were coming on, the bud was green, and even when it opened, it was still green, not yellow. Really weird! I was so sad, because they are the most beautiful flowers I have ever had in my garden. Why did they not turn yellow when they bloomed?

This can be caused by excess nitrogen or not enough sunlight.
https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/green-calla-lily-blooms.htm