For some food, the color shows the character and it is an important criterion to determine the fresh of food. This paper presents an optical method to measure the food color for determining the fresh level, the processing quality and distinguishing the true from the false of the food and so on. The reflection spectrum is used to measure the surface color of solid food and the principle to deal with the color in digital is discussed. As an example, the fresh of meat is change along the inductor of meat chromo protein, but it is difficult to measure the inductor because it exists as mixed along with the time. In this paper, the digital model between the hue and the inductor of meat's chromo protein is made, and then the model appraises the fresh of meat. The feasibility of the method is proved by the test using relationship of the meat's color and its fresh.