Color Change in Roses
What makes a rose change color? Is there something lacking in the soil?
I have a red rose
that turned pink and a yellow and red rose
that turned white.Botanical Journeys Plant Guides
There is nothing wrong with your soil. Many rose varieties simply do not hold their color well under certain growing conditions.
The weather is the most important causative factor in rose flowers turning different colors.
Just as roses tend to bloom more heavily during
cool weather, the flowers of some types will be a more intense color then as well.
Heat tends to cause rose blossoms to fade or wash out. Some roses turn purplish or brown as they age.
These behaviors are variety specific. If this bothers you, look for roses which are said to hold their color well.
As far as I know, it is not possible to change the color of a rose by altering the pH of its soil the way you can with a hydrangea.
Imagine the fun we could have if it were!