This very small bud opened today on my most recent rose acquisition, Shirley's Bouquet. The magenta pink rose, as you can see, is an entirely different color from the the large rose blooms.

I've never seen anything like this before. What causes this to happen? Is it a sported bud that's reverted back to one of the parent colors?

Parents are Moonstone x Vol de Nuit.

Thanks for any info you can share about this.....

Is the pink bloom on the same cane as the white one? If not, where does its stem originate?

Yes...a small stem growing from the same cane as the white rose bloom.