When Elayne Willis first saw Army Spc. Jeremiah D. Costello walk into her high school classroom, his hair almost threw her off.

“He was my first student to have colored hair. It was either green or blue all the time,” the English teacher recalled. “I thought, ‘Oh, my!’ ” But she quickly understood the kind heart that lay beneath the seemingly outlandish appearance. “He was the nicest boy, and he always had a smile,” she said.

Costello, 22, of Carlinville, Ill., was killed June 2 near Qayyarah, Iraq, when his vehicle struck an explosive. He was assigned to Fort Bliss, Texas.

Willis described Costello as a “special boy” who was always polite in class. “He...