I call it cream white, sometimes more yellow, others more white. 7.5", 40" tall, medium-late, lots of flowers. Great flower, would love to know it's name.
Try - SO LOVELY - as your photo + description matches
my clump quite well.
That is a beauty.
All the pictures I saw on the internet seem to match it perfectly. The only thing different is mine is a larger bloom by far. So for now I'll call it So Lovely.
I was going to suggest So Lovely too. I see Tinkers lists it as 6", mine is much larger as well though.