Know the facts – What is significance of the colours of the Olympic rings? 

The Olympic flag is a white background with five interlocking rings, in five different colours, to represent five continents united by the games - Europe, Asia, Africa, Americas (representing both North and South America) and Australia.

The colours were chosen by the International Olympic Committee. Some people have assigned particular colours to the particular continents but this idea was dropped in 1951 because there was no evidence that was the original intention of Pierre de Coubertin and the colours were not the colours used for those continents on the world map.

According to Coubertin, the colours of the rings together with the white of the background included the colours composing every competing nation's flag at the time.

Upon its initial introduction, Coubertin stated the following in the August 1913 edition of Olympique:... the six colours [including the flag's white background] combined in this way reproduce the colours of every country without exception. The blue and yellow of Sweden, the blue and white of Greece, the tricolour flags of France, United Kingdom, the United States, Germany, Belgium, Italy and Hungary, and the yellow and red of Spain are included, as are the innovative flags of Brazil and Australia, and those of ancient Japan and modern China. This, truly, is an international emblem.

Inputs from Olympic website, Wikipedia, other online sources