I have exactly the same situation! I divided a peony last fall and now both plants are in bloom: one is dark pink and one is white (the original plant was a light pink).
My mother suggested that I had somehow managed to divide the color factors up :)
They are in very similar locations, with same soil and sun.
Hopefully somebody comes along that can answer.

Cynthia

Some peony species change colors as the flower ages. Others form different colors on the same plant. (Mr. Ed comes to mind).

I've also read that the amount of sunlight impacts how long the bloom lasts....I only have Sarah Bernhardt right now and noticed that the flowers on the plants that receive 6 hrs of morning and afternoon sun are paler in color and shorter lived while those in light shade that receive about 3-4 hours of afternoon sun have a richer pink color and last longer.

Its been a trade off so far--earlier blooms if planted in full sun, but a shorter flowering period.

Hi. My only peony is a baby and won't bloom for a year or two but I was curious about your question so I did a quick Goggle search using the words "peonies color change" and came up with some articles about the same topic.

I don't know how to make a link so I'll just copy and paste. Here is the first:

Q) Sun, 3 Jun 2001
Do peonies change color as the bush gets older? I have been told that they do. My mother has several peony bushes and she thought they were red when set out and now they are white. I told her that they were probably always white but she says they were not white when they first bloomed.
MLW
A) Dear MLW;
The simple answer is 'NO, peonies do not change color' - a red peony is always a red peony.
Memories are not accurate, but sometimes they appear to change colors because of interlopers. People do not realize it, but peonies make seeds. These seeds usually fall down in the soil next to the parent plant. They are usually not even noticed, and may take 3 or more years to grow to flowering size. Since the seedlings foliage looks just like the parent, they are not noticed until they bloom.
Seedlings may be a different color from their parent so a 'red' peony can produce a seedling with white flowers. You may notice a variety of colors in old plantings all
originally one color.
So you just have to pay more attention to your plants. Look around the base of older peonies and you may see seedlings from this year with only one small leaf and year old plants will have a small stem or two, etc.
Good luck Jim W.

And the second:
Q. My yellow peony went white right after a late cold snap. What happened? Can peonies change color?
A. Yes and no. The truth is that peony plants don't change in bloom color, but they do seed, and the seedlings often will bloom a different color. As peonies grow and expand, it's easy to confuse the parent plant with some of the new volunteers that come along. Look closely at the base of your plant and you may see that the white flowers are coming from a stem that's separate from the original base plant. Sometimes the seedlings are more vigorous than the parent plant, and may take over the "look" of the peony bed.

If your peonies have been growing undisturbed in the same spot for three years or more, they may have become overcrowded. The best time to divide them is in the fall when the plant is about to go dormant. If the time is right, you'll see new growth buds at the crown of the bush.

Cut back the foliage, and dig out the entire clump. Cut the crown in several pieces, allowing each crownlet to have three to five eyes. Don't cut the thick part of the roots. If you want to hedge your bets, dust the cut surfaces with a fungicide. Plant so that eyes will be facing up, two inches below the soil surface, in moist, well-drained, rich soil in full sun. Water well and mulch.

Although peonies bloom for only a week or two in the spring, you can extend the season by planting early-, mid- and late-blooming varieties. Enjoy!

I hope this helps. I also read that sometimes there can be a "sport" or mutation that possibly is brought on by excessive heat or pollution but from the article it unclear whether this was referring to a single flower or the whole bush.

Kimberly

At my previous address I had a Peony which was there when . I lived there for 29 years and after several years the blooms suddenly turned dark red. this was not gradual , one year they were pink next they were dark red. Think there is something kind of clever with peony's. I didn't do anything to what so ever......It just happened. We moved 4 years ago and in 2015 I bought a new Peony, it has flowered this year for the first time and is a gorgeous pink with a tiny fleck of dark red. So look forward to see how this one develops over the coming years.

My peonies have been cream foryears, this year theyve cone out pink, so the answer is YES!