The Color window is a place to create and and manage two types of color palettes:
To add a swatch, drag the color swatch from the Color Widget above into the Library Palette.
To add swatch colors to Shapes:
Drag a swatch directly onto a Shape in the Viewport.
Drag swatches from the palette onto the Fill or Stroke Color attribute in the Attribute Editor on a Shape (Fill or Stroke tab).
With a Fill or Stroke Color attribute selected on a Shape, click a swatch.
You can also manually create your own Library Palettes 👇
New Palette... - create a new palette.
Library - select the library of palettes to load into the Library Palette drop down menu.
Import... - import an existing palette.
Save As... - save a version of the palette.
Rename Palette... - rename the palette.
Reveal in Finder/Explorer... - reveal the palette within your file system.
Set Gradient from Palette - set the color stops for a Gradient attribute selected in the Attribute Editor.
Create Array from Palette. - create a Color Array pre-populated with the colors in the palette.
Color swatches in the Scene Palette are nodes and therefore can be used to create shared connections between shapes. They are also saved with your scene.
Rollover a swatch and use the Connector (the connection anchor will appear on rollover) to create a connection to any Element that has a Color attribute.