One of the most powerful tools in Adobe Lightroom is the ability to make “Local Adjustments”. This is done by masking the area you are going to change in the photo and can be visualized by turning on the “Show Selected Mask Overlay” by clicking in the checkbox in the tool bar at the bottom of the work window, or by simply pressing the “o” key.
By default the color of the mask is red which in many cases works just fine. If we wanted to mask only the sun in this image to add some more contrast, we could not see the mask very well due to the red color of the sun.
Be sure that the “Show Selected Mask Overlay” is turned then by pressing “Shift-o” on the keyboard we can change the color of the mask making it easier to see.
By changing to the green overlay color I can now see that I did not quite get the entire edges.
Each time you press the “Shift-o” you will change to the next color of mask, the four colors are Red, Green, White, and Black.