THE RAINBOW FLAG  
in basel, switzerland, at the international co-operative
congress of world co-op, ICA leaders made plans for the
very first international ‘co-operators' day’ in essen, germany
which was held in july 1923.
they wanted to identify and define the growing co-operative
movement's common values and ideals to help unite
co-ops around the world by developing an international
co-op symbol to celebrate the movement's ideas of
international solidarity, economic efficiency, equality,
and world peace.
it is said that the meaning of the 7 colors of the rainbow flag is:
RED stands for courage.
ORANGE offers the vision of possibilities.
YELLOW represents the challenge that GREEN has kindled.
GREEN represents growth, a challenge to co-operators to
strive for growth of membership and of understanding of the
aims and values of co-operation.
SKY BLUE suggests far horizons, the need to provide education
and help to unfortunate people and to strive towards global unity.
DARK BLUE suggests pessimism, reminding us of less
fortunate people in the world who are in need of the benefits
from co-operation.
VIOLET is the color of warmth, beauty and friendship.

source : http://www.designboom.com/contemporary/peace.html