INDIANAPOLIS – Red. It’s not the color you normally want to see at the Indianapolis 500 presented by Gainbridge. After all, a waving red flag is what signals a stop in the race – such as what happened late in Sunday’s 103rd running following a crash involving six cars.

But there’s one exception when it comes to seeing red at Indianapolis Motor Speedway: the annual red carpet walk of celebrities attending “The Greatest Spectacle in Racing.” This year’s IMS red carpet drew some of the world’s most famous athletes, musicians and actors in the hours leading up to the race.

Highlighting the impressive list of celebrity attendees were Oscar-winning actors Christian Bale and Matt Damon, who served as honorary starters waving the green flag to begin the 200-lap race. Both were in awe as they surveyed the surroundings and mass of people at IMS.

“This is just ridiculous,” Damon told NBC on its prerace broadcast. “I mean, I have a lot of friends who’ve been here, and they told me that I wouldn’t be able to anticipate what this would be like. It’s awesome. I’ve never seen this many people in one place. This is really, really cool.”

Damon and Bale co-star in the upcoming film “Ford v. Ferrari” tracing the historic battle of manufacturers at the 24 Hours of Le Mans in 1966. Following that experience, Bale had a truer appreciation what the Indianapolis 500 drivers face on race morning.

“What I’m amazed at is that the drivers are able to concentrate at anything because you just want to scream in joy here,” Bale said. “The adrenaline is incredible; the excitement is amazing. How anybody manages to focus and just block this out is just stunning.

“Such appreciation for the racers that are here today, I’m in awe of every one of them pushing the limits of what’s humanly possible.”

Damon said he experienced a sense of pushing the limits when he rode with Mario Andretti in the INDYCAR Experience two-seat Indy car around the IMS oval the day before the race. Traveling nearly 200 mph with a wall inches away will grab your attention.

“I got to do a few laps with Mario Andretti and we were doing somewhere in the 190s,” Damon said. “It’s such an incredible rush and then you think about these guys adding 40 miles an hour to that, at least, and there’s 33 of them.”

Damon and Bale thrilled the crowd gathered behind the red-carpet barriers by signing autographs and posing for selfies with many of the fans. As for their job to wave the green flags in unison to start the race, the duo were excited to witness it from the flag stand overlooking the IMS yard of bricks.

“We’re going with the synchronized style,” Damon explained. “It’s a double green, I don’t know if it’s been attempted here before.”

To which Bale added, “We’ll just try not to hit each other in the face with it.”

Among the others walking the red carpet was NFL Hall of Fame running back Terrell Davis (shown at right), at IMS for his first Indy 500 as part of a sponsorship with Arrow Schmidt Peterson Motorsports.

“I came here last week and saw practice and I get it,” Davis said. “I knew about Indy, but I didn’t really know about it. Now I know about it.

“I understand why this is an event you must come to in your lifetime. It’s like the Kentucky Derby, The Masters, the Super Bowl, the Indy 500. You’ve got to come to this.”

Olympic gold medalist sprinter Justin Gatlin was backing another driver, Zach Veach of Andretti Autosport, but his mind was on all the drivers in the 500 field.

“It’s always a surreal feeling when you wake up and you know you have to go out and compete in an event that can change your life,” Gatlin mused. “I know all these guys and girl are going out there just trying to make their dream happen.”

Akbar Gbaja-Biamila and Matt Iseman, co-hosts of NBC’s “American Ninja Warrior,” said their hopes rested on the five NTT IndyCar Series drivers who have competed on the popular obstacle course challenge show: Josef Newgarden, Scott Dixon, Tony Kanaan, Helio Castroneves and Conor Daly.

“We’re rooting for all of them because they’re part of the ‘Ninja Warrior’ family,” Gbaja-Biamila said.

The duo admitted they were running on fumes, however, having spent Saturday night filming in Cincinnati.

“We took a helicopter to get here,” said Iseman. “We were not missing this event this day.”

Also drawing a loud cheer was famed tenor Jim Cornelison, the popular national anthem singer at Chicago Blackhawks NHL games who has become the new voice of the traditional playing of “Back Home Again in Indiana” that takes place just before the Indy 500 begins.

“I am loving singing here,” said Cornelison, who performed the song for the third time this year. “It’s such a fantastic venue and experience.”

Other impressive singers on hand were: Chevel Shepherd (shown at right), who won Season 15 of NBC’s “The Voice” and sang “God Bless America” before this capacity crowd; and Kelly Clarkson (shown below), the popular vocalist and one of the coaches on “The Voice" who sang the national anthem on Sunday.

Indiana Pacers center Domantas Sabonis, who drew a particularly loud cheer on the red carpet, was also making new memories at IMS. He said he was returning the favor of so many NTT IndyCar Series drivers who back the Pacers.

“Everybody comes out to support us,” Sabonis said. “The least I can do is support them.”

But it was racing legend Mario Andretti who commanded the loudest cheers on the red carpet. Celebrating the 50th anniversary of his 1969 Indy 500 win, Andretti was about to take actor Matthew Daddario of “Shadowhunter” on a thrill ride in the Honda “Fastest Seat in Sports” two-seater before the race.

“I’m really excited!” Daddario said of the upcoming ride.