Some stay yellow and might have yet another mutation or maybe combined two mutations. A different kind of instability is found in plants like H. 'Cynthia', H. 'Wollcott' and H. 'Freckles'. This mutation is however not often encountered in cultivars. Lastly K. Vaughn mentions that in H. 'Northern Mist' the variegation is transmitted 100 percent to its offspring even when crosses with a green plant. So this is a dominant mutation.
Plants differ in the broadness of the colored edge or center.
It may be a change in the number of cells in the meristem contributing to the different layers. Despite all of the above there are for sure other cases and exceptions, but the above covers the most encountered ones. Summary Mutation is an event that changes DNA which its offspring inherits and this can be in the flower and in a bud, and both in the nucleus or in the chloroplast. Recombination is an event that exchanges part of chromosomes leading to green or white in a yellow plant. Chimaeral rearrangement is an event whereby cells are exchanged between layers differing in color.