Zircon is a mineral of Zirconium Silicate and ranges in colours between colourless, to Yellow, from Red to Brown, Blue and Green.
In it's colourless state in high quality, it is known as "Matura Diamond" and is often used as a substitute for diamond although not as hard having a rating of 7.5 on the Mohs Hardness scale.
Pink, Red and Purple colours are made in natural states over hundreds of millions of years although heat treatment of natural Zircon can produce these colours at high enough temperatures. Zircon contains trace amounts of radioactive materials thus making them easily dateable and as they survive erosion and other natural hazards, they can be some of the oldest minerals - some in Western Australia thus far being the oldest datable minerals at 4.4 billion years ago.
Some Examples are shown below.