Some time later, Wilpon ran into Sandy Koufax and asked the Hall of Famer if he knew.
"The only think I can tell you," Koufax said, "is it was dirty." And the two laughed.
It was not until Wilpon crossed paths with Ralph Branca, who preceded Koufax in the Dodgers' rotation, that he found his answer. Branca recalled that the floor was made of terrazzo, a material with the look and feel of marble. And Wilpon, so pleased to have finally solved the riddle, ran to the phone to tell Jackie Robinson's widow.
"And it's beautiful terrazzo," Rachel Robinson said Wednesday, glancing around her.
And it's a beautiful rotunda, the jewel of Citi Field and, on Wednesday, the centerpiece of Major League Baseball's Jackie Robinson Day festivities. Amidst the grandeur of what is effectively a museum to honor Robinson, who broke baseball's color barrier 62 years ago, Rachel Robinson joined a panel of New York City and baseball dignitaries to officially dedicate the place.
Those in attendance swapped stories about Robinson's heroics in his fight for social change. And they lauded his widow, Rachel, whom Mets executive vice president of business operations Dave Howard called, "a woman who is American royalty."
Such a significant part of Jackie Robinson days past, Rachel Robinson has worked to perpetuate the memory of her late husband by establishing and working tirelessly for the Jackie Robinson Foundation, which seeks to develop leadership and scholarship among minority youths.
Jackie Robinson Day is a celebration of that, as much as it is a celebration of the man himself. And this new Mets ballpark -- with its rotunda inspired by Ebbets Field, home of the Brooklyn Dodgers, and named after Robinson -- provided the perfect setting for this year's event.
"This is a great day for us," Rachel Robinson said. "There's been talk about the challenges that faced us, and the things we've been through. I want you to know that on this day, I feel blessed. I don't feel like I'm a victim of anything. I feel strengthened by the life that we lived."
Greeting fans with two wide staircases and a high ceiling, the Rotunda displays black and white images from past decades -- Robinson running track at UCLA, Robinson graduating with his cap and gown, Robinson joking in the clubhouse with teammates. The photograph closest to the main entrance displays the outside of the Ebbets Field Rotunda.
"This is a great thrill, and it's also a little bit painful because all the old memories come flowing back into me," Rachel Robinson said. "When I look at the pictures of our family at certain stages or Jack's career at certain stages, I feel very emotional about it. But very positive."
In the center of the Rotunda stands a large "42," a tribute to Robinson's uniform number. And in a more transient tribute, every uniformed Major League player, manager, coach and umpire wore No. 42 on Wednesday, a uniform number that the league universally retired 12 years ago.
Players from the Mets and Padres, all those 42s, lined the field prior to Wednesday's game at Citi, while nine Jackie Robinson Foundation scholars gave a presentation of Robinson's nine cherished values: courage, excellence, persistence, justice, teamwork, commitment, citizenship, determination and integrity. A video tribute was presented on the center-field scoreboard. And as the scholars stepped in front of home plate, they were greeted by players from each team.
Then the No. 42s took the field.
Out in the entryway, fans were still filling in, a good many of them coming by way of the Jackie Robinson Rotunda. And that's just the point. When Wilpon installed the terrazzo and built the rest of the Rotunda, he wanted it to become a perpetual reminder of all that Robinson did for the game.
As inheritors of Dodger Blue and the team geographically closest to old Ebbets Field, the Mets consider themselves stewards of Robinson's legacy.
"It is appropriate that this rotunda -- open, living inclusive, a spot where all fans can come and congregate -- is a fitting tribute to the player who made us realize that baseball, too, can be inclusive," said MLB's president and chief operating officer Bob DuPuy.
"In dedicating this rotunda to Jackie Robinson, we are really dedicating it not just to him," said New York Governor David Paterson, "but to the memories of those Americans, both black and white, both Asian and Hispanic, both rich and poor, who have given their lives over the past couple of centuries to building a national movement that will bring economic, political and social justice to everyone who lives in America. Today, we honor one of those who was a trailblazer to that end."
There is still work to be done, as those in the sport are the first to admit. Despite Wednesday's news out of the Institute for Diversity and Ethics in Sports, reporting that the prevalence of black Major Leaguers has increased two percent over the past year, to 10.2 percent, the levels are not where baseball wants them to be.
But they are creeping closer.
"I feel encouraged," Rachel Robinson said. "And it's not a huge relief, but it's a step forward. I think we have to not only feel encouraged, but feel inspired by progress, so that we can not only sustain what we have, but work harder to see that we get that number up."
Perhaps the Rotunda, in its grandeur, can help inspire some youths to take to the game. If nothing else, it is an important reminder of the trials that one of the game's foremost social leaders faced every day of his life. As long as Citi Field stands, so too will that tribute.
"It's the permanency that we love, because when we're not here anymore, this will still be here," Wilpon said. "This is a forever place."
Anthony DiComo is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.