It won't be the soil conditions, but some of the newer varieties of roses do indeed change colour, and in particular, those which are peach or orange, changing to pink. Its usually because the new variety of rose isn't holding the genetic information for more than a couple of years, or even one year, and reverts to one or other of its parents.

On the other hand, if the flowers you're seeing are nothing like the original rose in shape and form, perhaps being open, single and cupshaped, you may be getting growth from the rootstock and the original grafted rose has died.

Have you ever seen the "Peace Rose?" I could swear sometimes it looks pink, other times yellow or even white. I also have the 'Hologram Rose,' same thing. Maybe it's my mood, the sun, who know. It's a different color every time I look at it. I'm OK with that too.

its not silly at all . there are fish that spend the first part of there life as males and over a certain size become female . if you change the water tempreture too quickly in a fish tank sword tails can change sex . as said most plants are man made as are dogs and many farm animals . they can always revert back . my acer tree always pushes big dark gren leaves and branches out that I have to cut off so it doesn't take over . goldfish change colour during there life quite often . you've only got to find some common land near you to see what actually thrives in your area and it wont look a bit like most gardens .

Once again Bamboo I have learnt something from your answer. Thank you ...I will still enjoy this rose, but will look again for a lovely orange (with copper leaves) in the garden centres to replace the one I removed. (I removed it along with all my plants to a holding bed while I barrowed in 4tons of soil improver. A job well worth doing with my heavy clay soil !)
Thank you too to my other responders.

The only silly questions are the ones not asked.