The tourmaline is a unique miracle of colour. The gemstone comes in green, red, blue, yellow, but there are also colourless specimens and black ones. Often two or more colours are found in a single tourmaline crystal. Also rare and very highly esteemed are tourmalines which appear to change their colour and cat's eye tourmalines. Having said all that, green is regarded as the classical tourmaline colour. If you ask a gemstone merchant about a tourmaline, green, in most cases, is the first colour he will think of.