Color science has provided a wealth of research that is useful in mapping and visualization. Cartographers use work on perceptual color systems, color vision deficiencies, surround induction, color naming, printing and display, and conversion between color systems. From this grounding, we structure our symbols to represent real-world phenomena so they can be discovered and understood by map readers. Color offers a three-dimensional structure which can be used to organize symbols for multivariate mapping. Mapmakers do not always have the color specification skills for this type of analytical design work, but color schemes offered on the Web at ColorBrewer.org provide starting sets that are structured to match the basic organizations of map data: sequential, diverging, and qualitative schemes.