The Eyedropper tool is used to create materials or palette color based on sampled colors in the 3D Viewport.
Create a new material with the Stroke Base Color to be the sampled color.
Add a new color to the color palette based on the sampled color.
LMB Create a stroke material.
Shift-LMB Create a fill material.
Shift-Ctrl-LMB Create both a stroke and fill material.