In May 1957, songwriter Bob Crewe saw a couple embracing through a windowshade as he passed on a train. He quickly set about turning the image into a song. Frank Slay, who owned the small Philadelphia record label XYZ with Crewe, added lyrics, and they soon had a complete song ready to record.

The Canadian pop group The Diamonds, who had experienced success with cover versions of other doo-wop records, quickly put out their own version of the song. They even used the same song, "Daddy Cool", on the b-side of their record as The Rays had. Their version received widespread radio play, also reaching the top ten of the Billboard airplay chart. However, it did not reach Billboard's sales chart, and only hit number 60 on the Top 100.

The song received a break when popular local disc jockey Hy Lit fell asleep with a stack of newly released records on his record player. "Silhouettes" happened to be the last to play, and so it repeated until he woke up. He began to play the song on his show. It became popular enough that Cameo-Parkway picked it up for national distribution.
~Source Wikipedia