A common question that we get is "why did my rose change color". The following is a short article on the subject.
It is not unusual for roses to "change color." A minor change occurs when cooler weather intensifies pink-to-red shades, or age and hot weather fade them. Knock Out ‘Blushing’ rose flowers, for example, are medium pink in cool springs like this and in fall, but a washed-out, nearly-white in summer. The 'Rainbow' and 'Sunny' Knockout rose marketing capitalizes on the fading of pastel pink and yellow petals as they age, emphasizing that at any one time there are deeply colored buds, pastel newly opened flowers, and pale to off-white older blossoms. The contrast is greatest, and those plants are most attractive in cool weather. Some of our Master Gardener volunteers have complained they are quite disappointed in the "washed-out" summer appearance of those varieties.
The second type of color change is due to the fact many roses are grafted, so the branches are one variety and the lower root system is a hardier rose. If those lower roots sprout branches, they may appear different in leaf size, shape and flower color. They are more likely to have such sprouts when planted shallow, or if the top branches are all killed by cold temperatures. The variety used for the hardy rootstock will survive cold damage but the grafted top may not. Roses may start out with branches and blossoms of a different variety such as a less hardy tea rose and end up with only the hardy root stock if the less hardy grafted top is killed out.
Adapted from an article in the Landscape Advisory Team Alert from Michigan State University: