A blue coloured single crystal CVD synthetic diamond material comprising: a plurality of layers, wherein the plurality of layers includes at least two sets of layers which differ in terms of their defect composition and colour, wherein defect type, defect concentration, and layer thickness for each of the at least two sets of layers is such that if the coloured single crystal CVD diamond material is fabricated into a round brilliant cut diamond comprising a table and a culet, and having a table to culet depth greater than 1 mm, the round brilliant cut diamond comprises a uniform colour as viewed by naked human eye under standard ambient viewing conditions in at least a direction through the table to the culet, wherein the at least two sets of layers comprise a first set of layers comprising boron dopant at a concentration sufficient to produce a blue colouration and a second set of layers comprising a lower concentration of boron dopant, wherein the first set of layers comprises an uncompensated boron dopant concentration no less than 0.01 ppm and no more than 5.00 ppm, wherein the second set of layers comprises single substitutional nitrogen dopant at a concentration of no less than 0.01 ppm and no more than 5 ppm, the concentration of nitrogen in the second set of layers being sufficiently low that it does not impact the overall blue hue of the layered single crystal CVD synthetic diamond material, wherein a figure of merit for visibility of individual layers is no more than 0.15, wherein the figure of merit for visibility of individual layers is calculated as the product: FM = layer thickness (mm) for the first set of layers x layer thickness (mm) for the second set of layers x solid boron concentration (ppm) in the first set of layers x round cut brilliant depth (mm). a plurality of layers, wherein the plurality of layers includes at least two sets of layers which differ in terms of their defect composition and colour, wherein defect type, defect concentration, and layer thickness for each of the at least two sets of layers is such that if the coloured single crystal CVD diamond material is fabricated into a round brilliant cut diamond comprising a table and a culet, and having a table to culet depth greater than 1 mm, the round brilliant cut diamond comprises a uniform colour as viewed by naked human eye under standard ambient viewing conditions in at least a direction through the table to the culet, wherein the at least two sets of layers comprise a first set of layers comprising boron dopant at a concentration sufficient to produce a blue colouration and a second set of layers comprising a lower concentration of boron dopant, wherein the first set of layers comprises an uncompensated boron dopant concentration no less than 0.01 ppm and no more than 5.00 ppm, wherein the second set of layers comprises single substitutional nitrogen dopant at a concentration of no less than 0.01 ppm and no more than 5 ppm, the concentration of nitrogen in the second set of layers being sufficiently low that it does not impact the overall blue hue of the layered single crystal CVD synthetic diamond material, wherein a figure of merit for visibility of individual layers is no more than 0.15, wherein the figure of merit for visibility of individual layers is calculated as the product: FM = layer thickness (mm) for the first set of layers x layer thickness (mm) for the second set of layers x solid boron concentration (ppm) in the first set of layers x round cut brilliant depth (mm).