Although color mutations on flower blooms seems pretty incredible, it is a common and naturally occurring phenomenon. Consider that most of the annuals and perennials are hybrids. A hybrid is created when two plants, generally of the same species, are cross pollinated either naturally or with simple human intervention. The resulting plant displays characteristics of both parents.
There are also naturally occurring mutations that create any number of variations in a plant. These mutations are typically not recurring. A sport, a mutation that is found to be stable, will sometimes be propagated as a new plant variety.
In any case, a bloom may occasionally be produced displaying the characteristics of the "other" parent. You may see an entire bloom of a completely differently color or a bloom with two different petal colors or color streaks. Typically the mutation is an isolated random occurrence, but certain hybrids my produce the mutation repeatedly, if not completely revert to the characteristics of one parent plant. For instance Pink Knockout roses often produce red blooming branches.
My Topaz Jewel Rugosa Rose is showing a bit of its' heritage. One of its parents is pink 'Belle Poitevine' and the other parent is yellow 'Golden Angel'.
After many years a pink rose showed up on my Red Ribbons rose. One of the parents is pink 'Walzertraum'.