A numerical grading system has been established for white gold alloys using the ASTM Yellowness Index D1925, an existing colour quality standard. The Index is calculated from the CIE (International Commission of Illumination) Tri-stimulus values, X, Y and Z, and the scale is linear, so that as the number decreases, the alloy becomes whiter. This Index provides values that have good correlation with visual assessments and permits easy differentiation of colour without knowledge of an alloys composition. The use of a spectrophotometer instrument provided a quick means of sample colour measurement, with high precision and accuracy.