Rainbow flag Alliance (ICA) designed an international co-op symbol and a flag for the first "Co-operators' Day," which was held in July 1923. After some experiments with different designs, a famous French cooperator, Professor Charles Gide, suggested using the seven colours of the rainbow for the flag. He pointed out that the rainbow symbolized unity in diversity and the power of light, enlightenment and progress. The first co-op rainbow flag was completed in 1924 and was adopted as an official symbol of the international cooperative movement in 1925. In 2001, the ICA's official flag was changed from a rainbow flag to a
Rainbow as "blue" would today be regarded as cyan, and what Newton called "indigo" would today be considered blue. The colour pattern of a rainbow is different from a spectrum, and the colours are less saturated. There is spectral smearing in a rainbow owing to the fact that for any particular wavelength, there is a distribution of exit angles, rather than a single unvarying angle. In addition, a rainbow is a blurred version of the bow obtained from a point source, because the disk diameter of the sun (0.5°) cannot be neglected compared to the width of a rainbow (2°). The