My understanding is that while chlorophyll = green is the primary photosynthetic system plants utilize, there is a secondary route that uses yellow. Thus yellow variegated plants grow reasonably vigorously. White being the absence of pigment, white variegated plants are less efficient, grow more slowly, may revert to all-green - Hemerocallis 'Kwanso' and Kerria japonica 'Picta' as examples. Also, variegated plants fertilized with additional nitrogen may change to all-green. Not certain if this applies to yellow-variegated, white-variegated, or both. Judy