A color group is an organization tool that lets you group together related color swatches in the Swatches panel. In addition, a color group can be a container for color harmonies, which you create using the Edit Colors/Recolor Artwork dialog box or the Color Guide panel. Color groups can contain only solid colors that include spot, process, or global colors. Gradients and patterns cannot be grouped.
You can use the Color Guide panel or the Edit Colors/Recolor Artwork dialog box to create harmonious color groups. Using either feature, you can choose a harmony rule to instantly generate a color scheme based on any color you want. For example, choose the Monochromatic harmony rule to create a color group containing all the same hue, but with different saturation levels. Or choose the High Contrast or Pentagram harmony rule to create a color group with contrasting colors for more visual impact.
For inspiration, to share color harmonies, or to create color groups outside Illustrator, choose Window > Extensions > Kuler and click through the different color harmonies available.
For more information, see the Kuler website at http://kuler.adobe.com/.