To turn on mask overlay, you can use the shift + O shortcut to cycle through the different color options for the mask overlay. This lets you visualize which areas of the image you're editing with the adjustment sliders, as mentioned in a video about Mask Overlay Modes in Lightroom.
Here's a breakdown of the process:
- Keyboard Shortcut: Pressing Shift + O will cycle through various overlay colors.
- The colors typically include red, green, black, and white.
- A custom color option is also available.
- Purpose of Overlay: The mask overlay visually displays which parts of your image are being affected by the selected editing mask. This helps you precisely target the areas you want to change with your adjustment sliders.
Essentially, there is not an "on" or "off" switch, but rather a toggling of different overlay colors. To "turn on" a mask overlay, use the shortcut shift + O until you find a color you like.
