Abstract: The concept of measurability design is innovatively applied to the optimization and upgrading of the colorimetry primary standard. From the perspective of stakeholders, the colorimetry primary standard device is regarded as an integrated measurement system. The metrological requirements throughout its life cycle are captured and classified, and key metrological parameters such as Lambertian property, density uniformity, integral sphere radius, and aperture coefficient are accurately identified. Measurability design is carried out around the key parameters, and verification experiments are conducted. The measurability design and verification process of the key parameter of Lambertian property are introduced in detail, achieving closed-loop control of the reference whiteboard process. The experimental results show that the expanded uncertainty of the colorimetry standard is improved to 0.0035 (k = 2), which enhances the measurement ability of the primary standard. This provides a more reliable metrological guarantee for the realization and transfer of the primary standard's quantity value and its participation in international comparisons.