Credit: Alex AspreyToday, May 12, marks the 50th anniversary of the release of “A Whiter Shade of Pale,” the memorable debut single by British prog-rock act Procol Harum.

The soulful, lyrically enigmatic tune — does anyone know what “skipped the light fandango” actually means? — is easily is the group’s biggest hit, spending six weeks at the top of the U.K. charts and reaching #5 in the U.S.

Over the years, “A Whiter Shade of Pale” has been used in many films, perhaps most famously in 1983’s The Big Chill, and has also became a popular wedding song. Procol Harum frontman Gary Brooker, who co-wrote the tune, is hard-pressed to explain why it’s so enduring.

“That is a big mystery. A mystery that I don’t think we can quite understand,” he tells ABC Radio.

Brooker notes that the song is “rather bizarre and off the wall,” and has “a haunting quality going on behind it.” He asks, “Why would somebody have it at their wedding? Why would somebody have it at their funeral? Why do people not forget it? Why do they know what they were doing when they first heard it?…If somebody finds the answer, I’d be glad to hear it.”

The singer/keyboardist, who continues to lead the current incarnation of Procol Harum, adds, “Maybe it wasn’t like anything that had come before, in the way of rock songs, pop songs…And maybe there hasn’t been one like it since, so it still stands out.”

Procol Harum released its first studio album in 14 years, Novum, last month. The band is winding down a brief U.K. trek in support of the new record, and will head out on a tour of continental Europe in September.

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