A flood of purple filled the 1600 block of West Jefferson Street on Saturday.

Members of the Omega Psi Phi Fraternity Inc. gathered in North Philadelphia to celebrate the unveiling of a Pennsylvania historical marker in honor of Oscar James Cooper, a medical doctor and cofounder of the historically Black fraternity.

They were also there for the renaming of Jefferson, between 16th and 17th Streets, to Dr. Oscar J. Cooper Way.

A few hundred men, members of the Greek letter fraternity, were dressed in purple sweaters, purple hoodies, and purple business blazers.

Many sat in folding chairs set up in the middle of the block, which had been closed to traffic. Men who wore dark business suits sported purple ties. And a bicyclist came dressed in bike shorts and a purple tank top.

“You own the color purple,” Nancy Moses, chair of the Pennsylvania Historical & Museum Commission, told the crowd after saying she had done a bit of research on the fraternity. “And I hear you give the best parties.”

The fraternity members had come in the traditional purple and gold of Omega Psi Phi to celebrate the unveilings at 11:17 a.m., a time set to mark the date the fraternity was founded on the campus of Howard University, on Nov. 17, 1911.

The marker was unveiled outside Cooper’s former home and medical office at 1621 W. Jefferson St. Purple and gold balloons fluttered in the wind at the corner of the residence, at Jefferson and Willington Streets.

The Pennsylvania Historical & Museum Commission and Philadelphia City Council worked with Mu Omega, the Philadelphia chapter of the international fraternity, to install the marker.

Cooper, born in Washington in 1888, cofounded the fraternity at Howard when he was a college junior with two fellow junior students, Bishop Edgar Amos Love and Frank Coleman, and their faculty adviser, Ernest Everett Just, a noted biologist.

After completing college and medical school, Cooper moved to Philadelphia and established a 50-year practice. He died in 1972.

He was also the initiating founder of the Beta Chapter of the fraternity at Lincoln University in 1914 and of Mu Omega in 1920.

His civic engagement expanded beyond fraternity life.

He was a founder of the Pyramid Club, at 1517 Girard Ave., in 1937. It provided Philadelphia’s Black professionals the opportunity for social, civic, and cultural events because segregation kept them from gathering in many Philadelphia restaurants and clubs.

Marian Anderson and Duke Ellington were among the musicians who gave concerts at the Pyramid, and artists such as Dox Thrash were able to have art shows there.

The building at 1621 W. Jefferson St. is owned and was restored by Jeffrey Smith, president of the Union Housing Development Corp. It now houses the Philadelphia offices of State Sen. Sharif Street.

“It is an honor when I come to work here and sit in the office that Dr. Cooper occupied,” Street said at the ceremony.

David E. Marion, the 41st grand basileus, or president, of the international fraternity, came from Mississippi. He said Omega Psi Phi is one of the largest fraternities in the world with more than 30,000 financial members.

Marion noted that it was amazing that Cooper provided medical services to members of his community “whether they had insurance or could pay for it themselves.” That generosity leaves an example for himself and others to follow, Marion said.

Mark A. Edwards Sr., president of Mu Omega, said he hopes the new marker and street sign will provide inspiration for young men who live in the surrounding blocks.

While many people think of the fraternity’s undergraduate school reputation for having parties and performing step shows, the organization’s members are mandated to provide community service.

“We are not just about stepping and having parties, we are committed to service,” Edwards said after the ceremony.

Phyllis Crump, a niece of Cooper, traveled to the unveiling with her daughter Debbie from their home in Morristown, N.J.

She grew up in Virginia and as a teenager would spend her summers with her uncle and aunt, who had no children, Crump said. She pointed to a narrow window on the second floor of the large building’s west side and said it was where her uncle’s office had been.

“It would have meant so much to him,” she said of the new tributes. “It’s such an honor.”