The Eyedropper tool allows you to set the stroke color by clicking the mouse on an area of the desired color. Simply select the eyedropper tool, then click the mouse anywhere on the computer screen that has your desired color. Once you've selected your color, the Select tool will be selected.

You can click on other windows/applications to select a color with the eyedropper, but do realize that clicking the mouse on other applications may cause them to use that mouse click.