Larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), exhibit a body-color polymorphism that is most distinct in the final instar. Larval coloration was investigated in relation to the effects of host plant diet. Larval coloration was strongly influenced by the plant parts on which larvae fed; larvae that fed on leaves exhibited a higher frequency of green coloration than larvae that fed on flowers and fruit. This pattern also was exhibited in full sibling larvae that had uniform genetic background. Larval performance in terms of survival, developmental period, and pupal weight was better in larvae reared on fruit than in those reared on leaves. Our results suggest that larval coloration was determined primarily by the portion of the plant upon which larvae were reared. Larvae also had a certain degree of plastic response to the diet change, which indicates larvae can adjust body color as they change the part of the host plant where they feed. Although the adaptive consequence of similar body color to plant part is still unknown, diet-induced body-color polymorphism in H. armigera might have some role in helping larvae avoid visual predation.