Paul McCartney delved deep into yesterday on “The Late Show” Monday. (See the clip below.)

Host Stephen Colbert showed the Beatles legend a photo of him and bandmate John Lennon collaborating on a song. The image inspired McCartney to revisit a period of time when observers had cast him as the bad guy in the breakup of the band.

“A lot of the talk was that I was the villain and that John and I didn’t really get on well ... and I kind of bought into it,” McCartney said. “When you’re called it enough, you start thinking, ‘Well, maybe I was.’”

McCartney said the picture reminded him that they were indeed friends.

“It’s a beautiful photo for me because it just reminds me of us working together and how cool it was,” he said.

The music legend, 77, said he thought of his late pal Lennon a lot.

“I dream about him,” McCartney said. When Colbert asked him to share a specific dream, McCartney jokingly retorted, “No.”

“When you’ve had a relationship like that for so long, such a deep relationship, I love when people revisit you in your dreams,” the icon continued. “I often have band dreams. And they’re crazy, and I’m often with John and just talking about doing something.”

“I have a lot of dreams about John, and they’re always good,” he added.

Some of the dreams involved his “bass covered in sticky tape,” said McCartney, who was on the show to promote his children’s book, “Hey Grandude!” We’ll let him explain below.