1/2 &1/2 Rose
I have a Knock Out rose bush 5 years old. It produces beautiful red blooms every year. This year on 9/27/19 it produced 1 bloom of 2 colors (red & pink) split perfectly down the middle. I have another bush about 20 feet away that once or twice a season will produce a bloom completely pink while all the others are solid red.
How is this possible?
Can one be effecting the other somehow?
I admit I am puzzled by the split-color rose. It's beautiful. You might contact a breeder to see whether that grower has an explanation. All the research I have done so far gives me no information on that. However, color changes are more easily explained.
Few commercially sold roses are pure stock, meaning the bush is the same from the roots to the blooms. Most often, the breeder begins with hardy root stock that is bred for endurance, such as being able to grow in all soil types and withstanding fluctuations in temperature. Onto that is grafted rose bushes with desired qualities such as appearance, fragrance, length of bloom time, shape, disease resistance. After a period of a few years, grafted stock can die. Your roses would then take on the root stock's color. To tell whether that happened, follow the new canes to their point of origin. If the cane starts below the soil level, it's likely the grafted stock has died and root stock is taking over. If the canes emerge above the graft it's likely that the root stock is just overproducing. If that is the case, cut the new canes off at the point where they join the grafted stem. Otherwise they will sap the strength of the graft and you could lose it.
Another possibility is that you have a sport. This happens when canes emerge above the graft, resembling the grafted plant but with a new color and/or shape. There is nothing wrong with the plant; it has simply mutated. Some growers keep these sports and turn them into new breeds of roses.
Finally, roses fade when it is hot. Tthe plant simply doesn't have the oomph to feed all the needs of the entire plant. Color is not necessary to survival, so it will divert energy from the bloom, the color taking a few steps down the vibrancy scale. When the weather cools off, the colors should bounce right back.
Here are a couple of resources for you to dig deeper if you wish.