The banding of color on the leaves is called intervenial chlorosis, and if left unchecked can grow to general chlorosis, or a complete yellowing of the leaf. Chlorosis is typically caused when leaves do not have enough nutrients to synthesise all the chlorophyll they need. It can be brought about by a combination of factors including:
-a specific mineral deficiency in the soil, such as iron or magnesium
-deficient nitrogen and/or proteins
-a soil pH at which minerals become unavailable for absorption by the roots
-poor drainage (waterlogged roots)
-damaged and/or compacted roots
-pesticides and particularly herbicides
-exposure to sulfur dioxide
-overabundance of calcium in the soil

Best of luck
JSG