The pattern of variegation on this plant is evidence of a sectorial chimera. This is where the plant has cells with two different genetic make ups, normal and variegated. In the case of this type of sectorial chimera the mutation that causes the colour difference is thought to be caused by what are known as permanent initial cells. These very special cells are found right at the very tip of growth and they remain there almost indefinitely. They regularly divide to form daughter meristem cells that further divide to make all the stuctures of a plant. Evidence suggests that there are usually only a few initial cells in a growing tip. When this type of sectorial chimera occurs it can give an indication of the number of initial cells by the ratio of the normal portion to the mutant sector. In this case it is probably one normal initial to two or three mutant ones that are the source of the variegate sector. Hope that makes a bit of sense.
The plant is A.scaphirostrus X A. retusus v.furfurceus c.v magnificus.
An interesting example of a different type of sectorial chimera we are familiar with is red apples. In this case the mutant sector is the outer layer of cells which in the case of the fruit produces red skin. If the cells on the inside of a red fruit are cultured and grown to maturity they will produce a tree with green fruit as the mutant sector is no longer present. This type of sectorial chimera is probably what is causing the odd flowers on the gymno pic I posted earlier. In that case the outer layers of cells have normal pigmentation and an inner layer, that gives rise to the cells that form a flower, has a different pigmentation. Here's that pic again will update it soon.