Business students need to steer clear of ethical “gray zones” as they seek big salaries in the corporate world, keynote speaker Rafael Rangel, Ph.D., told Thunderbird School of Global Management graduates Dec. 11 during the winter commencement. “Many of the great problems we have today started with small activities in what I call the ‘gray zone’ of what is and what is not ethical,” said Rangel, the parent of two Thunderbird alumni and president of Thunderbird’s partner school, Tecnológico de Monterrey in Mexico.