The leaves of some of variegated cultivars, so-called mutants have green and white or green and yellow sectors, (we would refer to that as variegation) but occasionally all white. These variations arise in a plant because of mutations in the nuclear or organellar genes of the plant. Sometimes this mutation occurs freely and other times mainly green leaves are produced.
The science behind it.
Leaf anatomy is radically altered in the green and white sectors. The cell sizes of the Mesophyll (the inner tissue of a leaf, containing many chloroplasts) are dramatically enlarged in the green sectors and palisade cells (Palisade cells are plant cells located on the leaves, right below the epidermis and cuticle. The chloroplasts in these cells absorb a major portion of the light energy used by the leaf) fail to expand in the white sectors. Where green sectors exist, they have a significantly higher than normal rates of O2 evolution (the process of generating molecular oxygen (O2) by a chemical reaction, usually from water) and elevated levels of chlorophyll. These changes in structure and photosynthetic function in variegated leaves are obviously part of a mechanism to compensate for a lack of photosynthesis in the white leaf sectors, whilst trying to avoid photodamage. Damage from light is common on the white, cream and yellow areas of variegated leaves and is often exhibited by scorching and subsequent necrosis (death of the affected parts).