The teenagers seeking shade as their tour groups crisscrossed leafy Harvard Yard on Thursday knew that they would be among the first students to feel the effect of the Supreme Court’s ruling on race-based admissions when they applied to colleges.

What they didn’t know was exactly how it would affect their chances. But many high school students, visiting Harvard University and beyond, said they were concerned to see long-established admissions practices giving way to something new and unfamiliar.

“It makes me more stressed about the whole concept of college,” said Danyael Morales, 16, a rising senior of Dominican and Puerto Rican heritage at Boston Latin Academy, a public school in Boston. “And with the whole agenda of not seeing race, I feel like colleges are not going to see me.”

The court voted 6 to 3 to reject affirmative action programs at Harvard and the University of North Carolina. The move is expected to lower the number of Black and Latino students at elite college campuses.

In Chapel Hill, N.C., most U.N.C. students are gone for the summer, but the student union swarmed with high school hopefuls trying on Carolina sweatshirts while their parents clutched admissions folders.

William Walker, who is Black, was visiting from Minneapolis to settle his son, an incoming freshman, at orientation. He discussed the decision with his family after the news broke. His daughter, a high school student, said it made her nervous about what college would be like for her, though Mr. Walker was not concerned, given her high grades and Advanced Placement classes.

He said his family would do their best to adapt. “You just adjust the fight. If Mike Tyson sends jabs to the gut, you rock and send uppercuts.”

Yosef Herrera, 16, a Hispanic high school student in Mercedes, Texas, said he supported the Supreme Court decision because he thought that affirmative action focused too much on race, often at the expense of other factors like ethnicity or family income. The policy can hurt people by inflaming racial divisions, he said.

When his time comes to apply to the Ivy League schools that he hopes to attend, Mr. Herrera, who is a co-chair of the High School Republican National Federation, said: “I think they’ll be fair. They’ll look at my application, and they’ll see what I’ve done as a person.”

Writing the majority opinion for the court, Chief Justice John G. Roberts Jr. said that universities could continue to consider the effect of race on the life experiences of applicants who wrote about it in their essays, as long as it did not become a substitute for affirmative action.

That adds another layer of difficulty to the already high-stress decision of what to write in college essays, said Dan Rubin, director of school counseling at Newton South High School in Newton, Mass. Mr. Rubin said he expected that many students would feel conflicted.

“It’s forcing kids of color to make a choice about which story to tell — a story about race, or about all the other things that make them a quality applicant,” he said. “Do they want to sacrifice the opportunity to talk about interning in a biotech lab?”

The essay was a concern for Mr. Morales, the Boston Latin Academy student. He was born in the Dominican Republic, learned English as a second language and hopes to attend Columbia University to study business. “I’ve already spent months learning how to write a college essay,” he said, “and I think this will alter my entire application process.”

Minhal Nazeer, 17, a high school student in Louisville, Ky., who plans to apply to colleges including Harvard and the University of North Carolina, said she would take advantage of the college essay to discuss her South Asian identity.

“I will be talking about my race in my applications to schools,” said Ms. Nazeer, whose parents immigrated from Pakistan. “And I hope they recognize that as an integral part of my identity.”

Matthew Wilson, a rising senior at Princeton University, said the court’s decision could lead to a better system, and more diversity. As it is, he said, the vast majority of students on his campus share the same socioeconomic background and ideological leanings — evidence that affirmative action has failed to create a true mix of backgrounds and ideas.

“Colleges ought to take the opportunity to view diversity in a different way, and look for more diverse upbringings and viewpoints,” said Mr. Wilson, whose father is white and whose mother immigrated to the United States from China.

Khymani James, 19, a rising junior at Columbia University who was raised in public housing in Boston by an immigrant mother from Jamaica, said he had braced for the court’s decision for weeks, trying to imagine what college would look like without affirmative action.

How, he wondered, would his recent history class on the Atlantic slave trade — where Black and white students swapped diverse perspectives — have felt different in a room where more people were white because of the end of affirmative action?

“It’s another attempt to try and erase race and erase racism,” he said, “like it doesn’t exist.”

Colbi Edmonds contributed reporting.