Reason for Colour in Diamonds

When ever we see a diamond,initially we come to a conclusion about its colour as Colourless or Tinted.Why we find one diamond as colourless and other as brown or yellow or any other colour.Why this difference?
Let us discuss

When diamonds contain interstetial imprities or structural defects,colour is observed.Diamonds are scientifically classified in to two main types and several subtypes

• Type 1: Contains nitrogen which is subdivided into Type 1a and Type 1b.
  • Type 1a: Nitrogen as clusters. Most natural diamonds fall in this type. It is further sub-divided into Type 1aA and Type 1aB depending on the arrangement of nitrogen atoms with or without a vacancy.
  • Type 1b: Nitrogen is present in a single state as foreign atoms. Almost all synthetic diamonds and a very small of natural diamonds fall in this type.
• Type 2: Contains hardly any nitrogen but contains other elements which are subdivided into Type 2a and Type 2b.
• Type 2a: No appreciable nitrogen, generally brown, pink and colorless.
• Type 2b: Contain boron and as a result such diamonds are semi-conducting. Generally blue diamonds.

In short if we conclude 

              

• Yellow/Brown colour in diamonds is due to Nitrogen and related color centers.
• Blue: Boron
• Green: Color center due to natural or artificial irradiation.
• Other colors are due to trace elements and related color centers.