Despite the interest in this pigment material, there have been no studies of the effect of substitution of Ba for Sr, which offers the ability to examine how the different site preferences of Ba and Sr affect the colour of the resultant apatite. Consequently, through a third year undergraduate mini-lab project, we investigated the effect of Sr doping in Ba10(MnO4)(PO4)5Cl2. The results show a unique member of the solid solution series, Ba6Sr4(MnO4)(PO4)5Cl2, which has a vivid blue colour attributed to this composition having perfect ordering between the Sr/Ba on the A1/A2 sites, and similar results are also shown for the Br analogue, Ba6Sr4(MnO4)(PO4)5Br2.