The Eyedropper tool Eyedropper Tool Icon is useful to pick colors from the image itself. It can be activated moving the mouse on the Eraser icon in the toolbar:

Eraser and Eyedropper group

Alternatively you can activate it pressing the I key or Alt+click. Using Left click will pick the color and store it as the Foreground color, using the Right click it will be stored as the Background color.


Color bar