This standard aims to provide an objective and quantitative method for evaluating minor color differences between coatings. It specifies the use of the CIE 1976 L*a*b* color difference formula for calculation, which effectively quantifies the degree of color difference perceptible to the human eye by converting measured color data into numerical values. Its implementation relies on the first two parts of the series of standards: first, the color coordinate values of the coatings must be obtained using color measurement instruments (such as spectrophotometers or colorimeters) according to specific principles, and then calculations must be performed using the unified formula specified in this part. This method is widely applied in the research and development, production, and quality control of coatings to achieve precise color matching and consistency management between batches.