Abstract: This study investigates diamond seed crystals, colourless, and pink CVD synthetic diamond samples sourced from two different companies. A comprehensive analysis was conducted using polarized microscope, DiamondView^TM, Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, UV-visible absorption spectroscopy, and low-temperature photoluminescence (PL) spectroscopy under various excitation wavelengths to systematically explore the colour origins and spectroscopic characteristics of the samples. All samples exhibited anomalous extinction under crossed polarizers, indicating variations in internal stress.DiamondView^TM images revealed that pink CVD diamonds displayed orange-red fluorescence dominated by NV⁰ centers, whereas colorless samples showed green fluorescence dominated by H3 centers. Infrared spectra classified the samples into type Ⅰ b. All pink samples exhibited a 1 450 cm^-1 (H1a) absorption peak associated with irradiation and annealing, while some also showed a 1510 cm^-1 peak related to high-pressure high-temperature (HPHT) treatment. Raman spectral analysis of the full width at half maximum (FWHM) of the intrinsic diamond peak at 1 332 cm^-1 indicated relatively higher crystalline quality in seed crystals, followed by colorless, and then pink samples. UV-Vis absorption spectra and photoluminescence spectra further confirmed the presence of NV⁰ and Si-V^- centers in the pink samples. These results demonstrate that CVD diamonds exhibit pronounced anomalous extinction and layered growth structures, and that the colour of pink CVD diamonds is primarily attributed to NV⁰ centers formed during irradiation and HPHT treatment, resulting in their orange-red fluorescence under DiamondView^TM images. The findings provide valuable reference for the detection of treatment processes and the determination of colour origins in CVD diamonds, thereby enhancing the accuracy of synthetic diamond identification and deepening the understanding of their spectroscopic formation mechanisms.