What is a case of an environmental effect changing a phenotype?

A. Caterpillars that receive two recessive traits from parents develop no wings as a defect.
B. Caterpillars with a parent with red wings and another with blue wings develop purple wings.
C. Caterpillars in cocoons under different colors of light develop different-colored wings.
D. Caterpillars with both parents having red wings develop red wings.