Answer: It's an interesting phenomenon, but there's no truth to the rumor that flowers change color because of close proximity to one another. What generally happens is that the stronger, more vigorous species overtakes its neighbors. Iris beds are a prime example. Some rhizomes die out and others expand from year to year. If a bed isn't dug and the rhizomes replanted, the more vigorous species will move in where a weaker (and often different color) iris used to be. The result is the old-fashioned purple instead of the hybridized colors. Your Christmas cactus will retain their original colors as long as all the plants remain healthy. If one dies out, a stronger species will take over the space and you'll notice a change in the flower color - not because the plant changed, but because the original plant died out.
Hope this clarifies things for you!
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