The notion of a white feather representing cowardice goes back to the 18th century, arising from the belief that a white feather in the tail of a game bird denoted poor quality. To 'show the white feather' was therefore to be 'unmanly'.
To give another man a white feather was considered a great insult amongst the nobles.
In 1914 the "order of the White Feather" was founded.
It encouraged women to give out white feathers to young men who had not joined the British Army.
You can read more about it here: http://www.spartacus.schoolnet.co.uk/FWWfeather.htm
There was a movie called "The Four Feathers" that came out last year I believe about the Brits in Africa around the turn of the century, too, if you're interested in related entertainment.