Abstract: The colour of precious metal alloys is an important factor that affects the appearance and personalization of jewelry. However, the industry lacks of unified requirements for the colour of the test conditions of precious metal alloys, which makes it impossible to accurately compare and trace the colours of the precious metal. Based on the problem of the inability to accurately compare the colour results of the precious metal alloys due to different testing conditions, spectral photometry was used to conduct experiments on four influencing factors: standard chromatics observers, instruments, sample sizes, and sample surface conditions. The change rule of colour space coordinates and values of colour difference are analyzed. The results show that both the calibrated spectrophotometer and colorimeter can accurately test the colour of the precious metals. The suitable testing conditions are CIE1964 standard colorimetric observer, with the sample size completely covering the instrument test hole, and the sample testing area being uniform, flat, clean, and defect free. The research results can provide a reference basis for the accurate testing of precious metal alloy colours.