Color is related to the optical power spectral properties of the stimulus detected by observers (Hutchings 2002). Cesia include transparency, translucence, gloss, luster, haze, lightness, opacity, and matt, and is related to the properties of reecting, transmitting, or diffusing light by foods evaluated by human observation. Spatial properties are divided into two main groups:

1. Modes of appearance in which color is modied depending on the angle of observation related to the light incidence angle, such as metallic, pearlescent, or iridescent materials

2. Modes of appearance related to optical properties of surfaces or objects in which effects of ordered patterns (textures) or nishing characteristics of food (as roughness, polish, etc.)

The color of foods can be studied in two main ways: chemically by analyzing the pigments present or physically by measuring the interaction of light. The last one is supported by objective values that consist of numerous combinations of tristimulus values such as Hunter Lab, CIE XYZ, or CIELAB (Pérez-Alvarez 2006a). The use of CIELAB color space was adopted as an internal standard using as illuminant D65 and 10º as a standard observer. L* is a measure of lightness, where 0 equals black and 100 equals white. High, positive values of a* indicate redness, and large, negative values indicate greenness; b* values indicate yellowness to blueness (AMSA 1991). C* is the color saturation, and hab is the hue. Another method to determine color is using reectance measurements. This is a good method for examining the amount of pigment and the pigments’ chemical state in situ. This technique closely relates to what the eye and brain see. With this method, repeated measurements over time can be made on the same sample. In addition, the procedure is rapid and relatively easy. In foods, reectance measurements are affected by food structure, surface moisture, fat content, and additives and pigment concentrations (Gallego-Restrepo, Pérez-Alvarez, and Ochoa 2010). Food structures are also associated with the light-scattering properties. Several foods colors can be described by their reectance spectra. The present chapter aims to review the basis of color changes during food fermentation of meat, sh, dairy products, and vegetables (olives).