Theres an easy solution for achieving color harmony: Use analogous color schemes. These are groups of colors that are related through one common color. When you look at a color wheel, analogous colors line up next to one another, with the common color being in the middle of the group. For example, orange, yellow and green all have the color yellow in common, and are therefore analogous.
Theres one important addition to an analogous color scheme, however: a complementary color. This is the color on the wheel thats opposite the one the analogous colors have in common. In the example of orange, yellow and green, purple is the complementary color to yellow. A complement can gray or mute your other colors, and in pure form (used sparingly) its a great way to create a point of interest.
Mark Gottsegen is an associate professor of art at the University of North Carolina at Greensboro and chair of the ASTM Internationals subcommittee on artists materials.