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.

Pick colors with right click

You can configure the Right click to pick colors from Edit > Preferences > Editor.


Color bar | Right-click