The whiteness of textile products is important in quality, in terms of controlling bleaching and in controlling visible whiteness. Whiteness is when the yarn or woven fabric is considered white. Generally, observers act in line with consumers' preferences. The average reflection in the visible region is considered a measure of whiteness. With the addition of the blue dye, the average reflection is reduced but the whiteness is increased.

Color is a phenomenon that differs depending on observation conditions. Depending on the source, direction, size, background and observer of the light, visual evaluation may be affected.

Measurements in laboratory environments using various tools are of course more accurate than visual comparison. Because the observation conditions are fixed in the laboratories, the brightness, the angle of view and the uncertainties depending on the observer are eliminated and the colors can be expressed numerically. The light in the laboratory has no effect on the measurement and the measurements are always made under the same conditions. In addition, international values ​​for color measurement have been determined by the International Lighting Board (L'Eclairage, CIE at Commission Internationale) and a method has been developed to provide various colors for this color measurement. This organization defined the light source and established its standards.

The whiteness index is the condition in which the color of an object appears to differ from the light source. Yarns or fabrics may also appear in different colors under different light sources, although they may appear the same color when viewed under the same light source. The whiteness index is the numerical rating of these color differences.

For physical tests performed in accredited laboratories, standards issued by local and foreign organizations are complied with. In this context, the following standards are used in color measurement analysis:

• TS EN ISO 105-J02 Textiles - Color fastness tests - Part J02: Evaluation of the relative whiteness with the instrument
• AATCC 110 Whiteness of Textiles (Test method 110)

These test methods are used to determine the whiteness and tone of textiles using formulas recommended by CIE.