|The Cosmopolitan here IS pink. Really. I've got bad lighting.|
There are too many versions of its origins - so you gotta take your pick as to which one you'd prefer to believe:
1) The Cosmopolitan Daisy, found in a bartending book from the 1930s, could've been its ancestor. While a lot of the basic ingredients were not quite the same, the end product was characteristically what today's cosmo looked like. Jigger Gordons Gin, 2 Dashes Cointreau, Juice of one Lemon, Teaspoon Raspberry (syrup)
2) Ocean Spray printed its version of Cosmopolitan in the 1960s called the "Harpoon" to sell more of its juice: 2 oz. cranberry, 1 oz. vodka or light rum or gin, over the rocks or tall with soda, with an optional splash of lime or lemon.
3) Apparently it was created by the gay community in the 1970s, by adding cranberry juice into a kamikaze.