A free online interactive tool called Color Scheme Designer lets you play with color relationships. You start by selecting the type of color scheme, such as monochromatic, complementary, or triadic (The small circles at top left).
You can dial the scheme around the wheel by placing your cursor onto the floating dark dot. In this way you can see how color relationships change. Here’s a set of cool analogous colors.
The color swatches on the right are from a complementary scheme playing blues against orange-yellows. The swatches that come out are automatically produced in a variety of values.
For the designer or decorator, this tool is an interesting way to stimulate new ideas and try things on for size.
Color Scheme Designer