Oblong-Winged Katydid (Amblycorypha oblongifolia), aka Bush Cricket - Middlefork Savanna, Lake County Forest Preserve District, near Lake Forest, IL - 23 July 2011
Wikipedia: "The color of the Oblong-Winged katydid is either green, tan, pink, or a dark tan or orange. Green is the most common amongst this species of katydid. Pink and tan are rare, but dark tan or orange is very rare. The origin of the unusual color stem from genetics, not from gender, age, or environment. The color is apparent from birth, and throughout their life."
Springfield Plateau Chapter of the Missouri Master Naturalist™: "The pink form of this typically lime green katydid was first described in 1887, and is said to occur in one out of every 500 individuals. Even more rarely they may be tan or brown. It is apparently a genetic variant as the New Orleans Audubon Insectarium bred a pink male and pink female, producing pink babies. Because of their rarity, this isn't as likely to occur in the wild. There are no other known abnormalities in pink katydids. This condition, called erythrism, is similar to the recessive gene present in albino animals. They are probably less likely to survive to adulthood, given their loss of camouflage."