Epson Perfection V500 - Manual (Page 125)

Select the cell that contains the hue you would like to use to adjust the color in your
image. This color now becomes the color of the center cell.
Note:
You can also use the cells to the right of the adjustment area to change the
brightness, if necessary.
Click the Color Applicator button. Your cursor changes to a droplet.
In the Preview window, click on the color in your image that needs adjustment. The color
change is reflected in your image.