Prior to 1951, the official handbook stated that each color corresponded to a particular continent:
blue for Europe
yellow for Asia
black for Africa
green for Australia and Oceania
red for the Americas (didn’t open, in accident)
this was removed because there was no evidence that Coubertin had intended it. (Wiki)
http://abcnews.go.com/blogs/headlines/2014/02/opening-ceremony-fail-just-four-rings-light-up-in-iconic-symbol/
not for T-shirt!
http://teespring.com/almostsochi