McCartney said “Baby’s In Black” was another attempt to write something “a little bit darker, bluesy…”
He was asked which of the two melody lines was the dominant one, so that it could be indicated on the sheet music who the lead singer was. He found it impossible to pick one out; most sheet music displays both. When singing the song solo, many singers use John's melody for the verse and Paul's for the bridge.
Formalistically, this one of the Beatle’s more verbose and complicated songs with its refrain, bridge, and guitar solo sections. Stylistically, it has an unusual mishmash of elements — the bluesy tune and choice of chords; the folksy almost hillbilly vocal arrangement.
“Baby’s In Black” is a waltzing lament that sounds like a cross between a sea shanty and a drinking song- with Harrison’s guitar playing the part of a drunken sailor. It consists of a four-line verse with chorus, the lack of middle eight which makes it difficult to classify it as a standard folk ballad.
Beatle scholar Walter Everett writes:
“Lennon continuously turns the volume knob of Harrison’s Gretsch to mask the attacks and create swells in the guitar line. It represents a collective second deliberate step towards the electronic manipulation of timbre that will mark the Beatles’ most colorful work over the next few years.”
The song tells the story of “baby in black's” boyfriend who has just died, and she still thinks of him, yet Lennon cannot stop thinking about her. The Baby in Black is sad because she is in love with a man who doesn't love her back and Mr. Lennon is blue when Baby in Black doesn't love him.
Some have said that "Baby” is Astrid Kirchherr an early friend of the Beatles who became the bands first photographer. The “Him” is Stuart Sutcliffe early member of the Beatles and Lennons’ friend who died suddenly in 1962.
In the line “She thinks of him and so she dresses in black/And though he'll never come back she's dressed in black,” Astrid is devastated by his death, but John knows he's not coming back.
John cannot get Astrid out of his thoughts, but he understands that her thoughts are with Stuart not him. He is in love with her- but “long will it take you see the mistake she has made” suggesting there may have been a competition for Astrid between John and Stuart.