Colour Picker Tool

Sampled (or picked) colours from the Colour Picker Tool are stored in the swatch next to the dropper icon on the Colour panel.

The following settings can be adjusted from the context toolbar:

Auto-apply—when enabled (default), the picked colour will automatically apply to the selected object's Fill or Stroke, depending on which colour selector is active on the Colour panel. When unselected, the picked colour is not automatically applied.
Radius—Choose to sample from directly under the cursor (Point 1x1) or from differently sized square areas where the colour is averaged.
Source—determines from where the tool can pick colours. Current Layer restricts picking to the currently selected layer; Global picks from all layers.