That was an AM radio classic in '67 in the U.S. "L'amour est bleu" (French pronunciation: [lamuʁ ɛ blø]; "Love Is Blue") is a song whose music was composed by André Popp, and whose lyrics were written by Pierre Cour, in 1967. Bryan Blackburn later wrote English-language lyrics for it. First performed in French by Greek singer Vicky Leandros (appearing as Vicky) as the Luxembourgish entry in the Eurovision Song Contest 1967, it has since been recorded by many other musicians, most notably French orchestra leader Paul Mauriat, whose familiar instrumental version (recorded in late 1967) became the first number-one hit by a French lead artist to top the Billboard Hot 100 in America.
Vicky Leandros' original version is worth a listen, too.