Eyedropper - Apply Fill Color to Stroke And Vice Versa

Copy the color onto the object using the eyedropper.

Use Shift X to swap the colors, or click where I circled red

If you just want only the stroke, then drag and drop from the tools palette the stroke. Deselct and shift X to swap colors if needed prior to drag & drop.

Shift X

Switches the color between fill and stroke.

One way - select the stroke (or the rectangle) and choose Add Selected Colors from the Swatches Pallet menu. The colors will be added to the pallet, and available for easy use.