The 12th-seeded duo defeated Spanish 11th seeds Feliciano Lopez and Marc Lopez 6-4, 6-3 to win their first US Open. Their other Slam trophy came at Wimbledon in 2015.
After the triumph, Rojer -- wearing a yellow shirt bearing a drawing of the Statue of Liberty -- said the clothing was inspired by last month's confrontation between extreme right demonstrators and counter-protestors in Charlottesville, Virginia, that left one person dead.
The Dutchman said he has another shirt with people locking arms in a civil rights march.
"Hopefully we're moving in that direction," Rojer said. "I've been here since I was 12 years old. It's a great country. I'm happy they let me in and that I get to do my job here.
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"Hopefully we'll create these opportunities for everybody."
His comments come as US President Donald Trump has tightened immigration policies and after he spoke of "very fine people" on both sides in Charlottesvile, shocking even some political allies.
Heather Heyer, 32, was killed and 19 others injured when a far-right supporter ran his car into the crowd of counter demonstrators.
"I just wanted to have the conversation going and promoting again, just freedom and justice, liberty for everybody on gender issues, on racial issues which we deal a lot with in this country," Rojer said.
"I feel in tennis we don't say much about it, but this is just tennis... And especially I think it's symbolic to be here."
"First time I noticed color was when I came to the US, sad to say that, when I was 12, because we don't grow up with that back home," he said.
"It's stuff I know that goes on. I read the news and I see a lot of unfair stuff going on. Some of these people don't have a voice to defend themselves and this kind of stuff, but it just really came about after Charlottesville and I thought it was a good message."
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Tecau added that as champion athletes they had an obligation to spread a message of racial equality and social justice.
"We're viewed as role models for a lot of the people," he said. "It's nice to send this message and spread it, because you have a lot of people that look up to you.
"It's important to see we're not just athletes competing for Slams and prize money and glory. In the locker room, everybody is the same. We're all friends and all compete against each other.
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