Adobe Illustrator

You can use Illustrator’s Eyedropper tool to load the attributes of existing objects quickly. This can be useful in two ways. First, if you already have an object selected when you click another object with the Eyedropper tool, your selected object changes to match the object you clicked. Second, you can click once with the Eyedropper to sample the attributes of an object, and you can then Option-click (Alt-click) to apply those attributes to other objects in your file without actually having to select them.

You can configure the Eyedropper tool to sample just the basic appearance of an object (the topmost fill and stroke) or complete complex appearances. To control what the Eye-dropper tool can sample, double-click the tool in the Toolbox. Double-click the Eyedropper tool in the Toolbox to control what specific attributes the tool uses for sampling.

Shift-click with the Eyedropper tool to sample colors from the pixels of raster images. In this way, the Eyedropper tool works much like the one found in Photoshop.