If you hold the Shift key down while the eyedropper is active, you can place color samplers on your image. These samplers allow you to continuously display color readings for specific points on your image. You can place up to four samplers in an image. Place a couple of sampler points on your image now and notice what happens to the Info Palette. It expands to show the sampler readings. These are useful for doing advanced color correction work.
You can also choose the color sampler tool directly from the toolbox (hidden under the eyedropper), but it is much easier to just remember I for eyedropper and shift for the sampler tool.
When you switch away from the eyedropper tool, the samplers will hide, but the color readings will still be shown on the Info Palette.
To remove a sampler, activate the eyedropper, hold the shift key down and move the cursor directly over the sampler target; the cursor will change to a pointer and then you can click and drag it outside of the document window.
To clear all color samplers at once, choose the color sampler tool from under the eyedropper in the toolbox, and then click "Clear" on the options bar.
