The ISO 5631-1:2013 standard specifies a diffuse reflection method for paper and Cardboard Color determination, suitable for indoor daylight conditions (C/2 °). This method calculates the Color characteristics of paper, including indicators such as chromatic value and whiteness, by measuring its reflectance in the visible Light spectrum. This standard applies to a wide range of paper and Cardboard, especially products with requirements for Color Appearance, such as printing paper and Encasement materials. It provides a uniform method for the standardized assessment of paper Color and is widely used in quality control, product development and international trade to help ensure paper Color conformity and Stability.