Controlling Transparency & Gamut Preferences:
For Windows - Edit > Preferences > Transparency & Gamut.
For Mac - Photoshop > Preferences > Transparency & Gamut.
Here you can select the Transparency Settings options you want to use.
○ Grid Size. Allows you to select a transparency grid size.
○ Grid Colors. Allows you to choose the color scheme for the transparency grid.
Select the Gamut Warning options you want to use.
○ Color. Choose a color to mask areas of an image that move out of the CMYK color space.
○ Opacity. Enter a value from 0% to 100%. Opacity determines how much of the Color Overlay masks the original image pixels.