This is a new one. Are you sure it is field corn or is it sweet corn? Are they all purple? My suggestion would be unless it is withered and bug eaten, watch, water and wait. It may a phase it is going through and weather may be affecting it. On the other hand if it stays purple it may not be sweet corn, but a purple corn. Usually you plant corn and get corn, sometimes you plant corn and get little ugly trolls. Mistakes do happen.