Primevere? Just a guess--a friend of mine has one that looks similar to this that she says is primevere. This from Buck Canyon Gardens: Peony Primevere is a anemone form peony, creamy white guard petals that may open with light pink coloring, and a canary yellow center that fades to cream.

Bowl of Beauty. A faithful heirloom peony. Here is a link that might be useful: Bowl of Beauty

What color is your tree peony in question? I ask this because digital cameras are not always very accurate with some of the reds. Yours looks more purple. Is that the case? Shima-nishiki is not purple at all. Below are a couple of pics of mine. The above picture is from last year, 2017. As you can see, it is not purplish. The next picture is from this year, a few days ago. In this one, you can see that there is a solid color flower, but it is red. It had evidently reverted back to its sport parent variety, Taiyo. It had 2 solid reds this year with 3 striped ones. I have seen roses do this that are sports also. They can revert back to their sport parents sometimes with incompletely colored flowers. The flowers on yours also look like they have more petals than mine, but that can vary between flowers. I have no idea what you have there, but it is pretty no matter what it is. Maybe this will help in some small way.

Thank you so much for your reply! Don't think it is bowl of beauty though...the one I have has much lighter guard petals and the whole thing has now faded to a pale pink and white. It's stumping me!