Queen Victoria forbid the Wearing'o'the Green, by soliders in the British Army. The simple act of wearing green on St. Patric's Day took on the meaning of support for either Home Rule or for a free Ireland. It was a punishable offense, I believe that it was considered treason within the British army. However,in the general populace, wearing green publically showed your support for actions aganist the British Government, which if nothing else, could direct unwanted attention to one's Republican activities.

There is also a very interesting piece of film footage of Harry Truman in the Pacific at the end of WWII, participating in a ceremonial presentation of the wearin'o'the green to himself, thus showing the US support for the Newly established Irish Republic.