Abstract: A symmetrical model of color visions--the decoding model--has been established for us to understand color vision better. It adopts new continuous value logic or fuzzy logic and works in a way very similar to the way a 3-8 decoder in a numerical circuit does. Unlike a popular zone model of color vision, the decoding model has four pairs of opponent colors: blue-yellow, green-magenta, red-cyan and white-black instead of three pairs: red-green, blue-yellow and white-black. By the decoding model, the evolution of color vision, color blindness and the perception of color appearance can be explained more concisely; Young and Helmholtz's tri-pigment theory and Hering's opponent theory can be unified more naturally.