Colorfastness refers to the ability of a material, such as fabric or dye, to retain its color when exposed to various conditions, including washing, sunlight, and rubbing. High colorfastness means that the colors remain vibrant and do not fade or bleed over time, which is especially important for textiles used in clothing and home furnishings. Testing for colorfastness typically involves subjecting the material to specific conditions to see how well it holds up. Common tests include the AATCC test for water resistance and the ISO standard for light exposure. Ensuring good colorfastness is crucial for maintaining the quality and appearance of products.