This factor is also fully expressed in the Simplex condition. When Yellow is also present the dark pigment changes chemically to become one of the highly desired RED shades. As a grower you have to be very lucky to have a whole plant sport or even a whole branch where it would be possible to get a cutting. Usually it is only a part of a bloom or even just a segment of a petal. The quite common streaking of a contrasting color on a petal, considered a fault when judging, is a most welcome bit of genetic evidence if you are a breeder.
Some varieties never do it, some do it often, and the Variegated types do it in every bloom.
This is only likely to happen if the color that disappears is Simplex. There is a certain likelihood of damage, of course, due to chemicals and radiation, but significant additional frequency is determined by the genes position on the chromosome. The closer to an end where crossover tangling can occur, the more often the factor is accidentally lost an the higher the frequency of a particular change. If the resulting cells which carry such a change form sufficient tissue, then a cutting may be had and the change secured. Usually, however, just a few cells in a growing row on a petal show the effect and the result is simply a streaked and spoiled petal.