No, soil chemistry has no bearing on the flower color of a clematis. Nutrient levels can have a bearing on the intensity of the color but that is more likely a factor of sunlight. Both very intense sunlight or a lot of shade can cause a fading or bleaching of the colors.

What kind of clematis is it?

Some clematis change colour significantly as the flowers age. My Niobe opens black-red, and after a few days in strong sunlight it turns purplish. Nelly Moser can't take strong sunlight either. It just turns into white.

the plant flower color can not change.. its genetic..

the flowers themselves can change .. as the tissue ages ...

or perhaps a cold snap did something to the bud

ken

Yes, colour is genetic, but genes can mutate, and it leads to new sports(mosaicism). It happens relatively often in chrysanthemums, tulips, roses and also some others .I have posted some pictures of such plants in one of my threads. Additionally, there are some unexpained changes of colour, it happened to me with an Echinacea plant(and it was not a seedling inside another plant).

It happens relatively often in chrysanthemums, tulips, roses and also some others

===>>> yes in the highly vegetative plants.. and those forced into incredible mass production quantities..

and once in a billion years on a established woody perennial ..

but yes.. its possible .. but most likely.. not probable ..

ken

A very common double clematis Multi Blue is just a sport from just as common The President. Soil chemistry(or other unknown factors ) can change colour on some Azaleas. I bought Azalea Gibraltar 3 times, with flowers on them, only because they were distinctly orange. In my garden they are all distinctly red.

Here it is on the right. When I bought it, it had the same colour as the orange eye of the yellow one.

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Thanks guys. I did notice today...the third bloom is the right color...so who knows????. It wasn't fading...the first two looked different right off the bat. And no cold snaps here. Unseasonably warm winter.

Whatever the case...I'm hoping the rest will keep in line with this third bloom.