They cannot change color....a biological impossibility.
What may have happened is some seeded and are more vigorous than the deeper colored ones.
If you don't like the color you have, dig them up and plant more of a color you do like....and be sure to dead head the new plants.
Linda C

I concur with Ginny :-) I had several colors too and now they are all white. I've only had mine about 6 years. Where the lavendar one was, there is still only one plant and it's now white. I've also had peonies change color from pink to white and then the next year pink again, then white another year. It was pink this year. I have no idea what causes it but I know for certain it's not more vigorous peony seedlings taking over. I wish someone could explain it!
VG

Hi Ginny,

I think it's something in the soil. We've got pictures of our landscaping from the first season after we purchased this place four years ago. We took the pictures to look at over the winters in deciding what we wanted to change. In front, there's a huge old rhoddie. In our pictures, it's a faint pinkish white...very unattractive & looks like used Kleenex hanging on the shrub. Last spring & this year, that darn rhoddie has turned out to be one of the old purple ones that we see everywhere around New England. Why the change? Who knows but I've got it on film! I gave it a foliar spray of Mir-Acid our second season in the house...is that the reason? I've got no idea but I sure believe you with your astilbes.

/T

These are definitely the same plants, not self-sown seedlings. I am on my hands and knees in that garden and I know what's going on out there! Wish I had the answer to this mystery. Astilbe is one of the few flowers I can count on for a good show of color in the shade and this is a real disappointment.

Maybe the soil or sun conditions have changed over time? Don't astilbes like at least some sun? And now, with a changing environment, the amount of sun has changed? Or soil amendments are lacking?

I don't know, just throwing some things out there. Some of your astilbes are 25 years old, you mentioned, so maybe they just peter out after awhile?

I have two smaller variety astilbes that I have grown in pots for several years - one red and one lavender. For the past two years both have come up lavender which is very disappointing. I divided one this spring and now have several LAVENDER plants! Guess I will have to give a couple away and replace with other colours. Three years ago I moved from a house where they grew in pots in mainly full sun, and now have a large patio garden where they are growing more in shade - could this have something to do with it ... I wonder.

some of mine have faded too.they are old and robust but this happened last year also

Very late to this party :-) Many common astilbe selections are actually hybrids of two or more species. It is entirely possible that the color changes noted are a reversion to the genetically dominant coloring of one of the parent species. This typically accounts for radical color changes noted in other plant types, like irises or glads. Even clematis.

The exception is certain species of hydrangea, one of the very few plants whose color is influenced by soil conditions.

Well, a great surprise to get more replies to my very old post. If some perennials can spontaneously revert, then who wants to spend a fair bit of money on a special cultivar? Is there a scientific article on this you could recommend, gardengal48? I'd be interested in reading it, if you know of one.

"Is there a scientific article on this you could recommend, gardengal48? I'd be interested in reading it, if you know of one."

Off the top of my head, no. But Googling 'genetic reversion' or 'genetic color dominance' should generate some appropriate literature.

"Also, regarding hydraengas (sic), ONLY the bigleaf species is capable of changing between pink and blue depending on soil conditions"

Mountain hydrangea, Hydrangea serrata, is recognized as a separate species from H. macrophylla and also has the ability to change flower color based on soil chemistry. As does. H. involucrata.

Hydrangea authorities, including Michael Dirr, Daniel Hinkley and the van Gelderens, as well as taxonomists distinguish serrata as a separate and distinct species from macrophylla due to differences in morphology and phylogeny. Virtually all the respected literature reflects the same. This has been common knowledge since the early 90's. As science progresses and plant DNA testing becomes more universal, old, outdated and incorrect assumptions are being corrected. We need to keep up with the times.

I moved last year and dig my three astilbes (gorgeous deep red last year) and they are a washed out pink as they are beginning to bloom right now. Very disappointed. I do think plants can revert, I've just only seen it in things like irises and aspidistra that keep pushing out new growth through a continually growing rhizome.

My astilbes did the same thing. Once a beautiful vibrant red now white and boring

This has just happened to my beautiful named Japanese irises. They have reverted to what looks like the species, plain purple and much smaller and less showy than the cultivars. I have three cultivars, one I bought almost 40 years ago, two sent to me about 20 years ago as a gift from Ego45, long a wise and skilled member of these forums. What could have happened? They have not bloomed well the last couple of years and now this. So disappointing....

I divided mine and moved one part to a shadier area and it changed from white to red. No idea why and, wasn't expected but a nice surprise. The it became a very deep rich red colour from a white variety. Very strange

I have to argre mine is a dirty purple !! 😱🇨🇮