This year, Colorado State University has reported finding multiple examples of racist graffiti and signs or fliers linked to extremist hate groups around campus. Last summer, a paper noose was found hanging in a residence hall.

In the statement, Dr. Frank said the school was trying to reach the brothers to reimburse them and offer to bring them back as V.I.P. guests. The school also needed to undertake broader changes aimed at inclusivity, he said.

What the Gray brothers experienced is not uncommon for many minorities, who report finding their very presence in some situations wrongly interpreted as a threat. Last month, two black men were arrested while waiting for a meeting in a Philadelphia Starbucks, sparking widespread criticism of the coffee chain and the city police.

During the 911 call on Monday, the woman who called said the brothers were “definitely not” a part of the tour, describing their behavior as “odd” and their clothing as bearing “dark stuff.” She accused them of lying by not giving their names or honestly answering when she asked what they wanted to study.

Later, she appeared to express some doubt, saying that “it’s probably nothing” and that she felt “ridiculous.” But she could not shake her suspicion, she said.

“If it’s nothing, I’m sorry, but it actually made me like feel sick and I’ve never felt like that,” she said. Her name was withheld by the campus police.