Munsell's system became extremely popular, the de facto reference for American color standards—used not only for specifying the color of paints and crayons, but also electrical wire, beer, and soil color—because it was organized based on human perception measurements. It specified colors via an easily learned and systematic triple of numbers. The color chips sold in the "Munsell Book of Color" covered a wide gamut and remained stable over time (rather than fading). The trouble with the Munsell system for computer graphics applications is that its colors are not specified via any set of simple equations, but only via its measurements: effectively a lookup table.