Every gemstone have our unique colour due to their material composition. When the light pass through the gemstone the some amount of light refracted due to this the color emits by the gemstone it will blue, green, red, purple etc. The coloured gemstone stone have different colour that make them special so that these gemstone can be used for different purposes. Which gemstone should be place on particular place like jewellery, or other place depends upon the fashion or astrology. Depends upon the requirement specific gemstone will be selected.