Pink is a rare colour for diamonds,but the Argyle mine has provided a consistent supply of the coloured diamonds allowing analysis into the origin of the colour.The colour is commonly confined to thin lamellae,as are brown colours.EPR measurements during photo-chromic alterations indicate electron transfers between isolated nitrogen centres and an unknown pink defect centre.PL using 633 nm excitation reveals a dominant PL peak at 661 nm associated with pink,and a peak at 710 nm associated with brown.Depending on the crystallographic plane,the 710 nm can be highly polarized,while the 661 nm peak is weakly polarized.CL images of pinks show texture,while micro CL reveals enhanced levels of H3 centres within pink lamellae and depleted levels of N3 centres,while FTIR mapping shows an anti-correlation of B-centres and pink colour.These CL and FTIR observations are consistent with B-centres having been involved in lattice slip events occurring along two different planes.It is postulated that the near-neighbour defects provide electronic energy levels favourable for interaction with another defect,possibly atomic,the identity of which remains a mystery.