Green peach aphids  (Myzus persicae) are one of the most common insect pests of tobacco.
Contrary to their name, not all green peach aphids are green. In fact, like many other aphid species including potato aphids  and pea aphids , green peach aphid has different color forms or morphs, ranging in color from green to red.
The source of this color variation has been studied most extensively in pea aphids , and it results of aphids co-opting genetic tools from fungi to synthesize carotenoids (the same pigments that make carrots and other foods orange).
Why do we care why red aphids are red? Because color seems to relate to other interesting, and potentially important, characteristics.
Red green peach aphids have been suggested to be more resistant to some insecticides (as have red potato aphids), and red color forms also appear to predominate at hotter, late summer temperatures in North Carolina.
A graduate student in my lab, Alejandro Merchan , is focusing on understanding the interaction between aphid diversity and insecticide resistance, color diversity included.