Most designers new to InDesign think the Eyedropper tool exists solely to choose a color from an image or other object on the page. More experienced users know just how powerful it can be, and much easier it can make things.
Not only can you choose colors, but you can apply fonts, styles, colors, transparency and more to other objects with simple clicks.
Take a look at InDesign Eyedropper Tool Tips over at CreativePro for a look at this highly useful tool.
If you work in Photoshop, you’ve probably used the Eyedropper tool at one point or another. Most users simply select the eyedropper tool and click on an area in the image to grab the color they want and that’s the end of it. But did you know there’s a more accurate way to select the color you want? When you use the Eyedropper tool, the default is to select one single pixel as a basis for the color you want to choose. So let’s say you want to choose the orange colored background in the photo above. If you use the eyedropper tool at it’s default, you might end up with a color you weren’t counting on due to the fact that there are many colored pixels that make up that orange, such as tan and brown, and the tool will only choose the one color that the curser is directly over. 
To get a better representation of the color you want, select the Eyedropper tool and go up to the toolbar and you will see “Sample Size” with a drop-down menu. Click the menu and select 3 by 3 average. This will look at a 3 pixel by 3 pixel area and average the colors to give you your selection, which is much more accurate and probably more closely represents the color you’re looking for.