The Transparency and Shading tab controls the grid size and color representing transparent backgrounds and transparent areas of layers. Additionally, this is where you set the color and opacity of the Crop shading area.
Grid size Chose one of the four grid sizes from the drop-down list.
Grid Colors Choose a color scheme from the Scheme drop-down list. To customize the grid colors, click inside the Color 1 or Color 2 boxes and select new colors.
Preview displays your proposed changes to the transparency grid.
Enable crop shading area Mark this check box to activate shading outside the crop rectangle.
Color Click inside the Color box to choose a shading area color.
Opacity Use the Opacity setting to control how opaque the shading area color will be.
Warning: When crop shading is enabled and you attempt to crop an 8-bit (256 colors) or less image, the area outside the crop rectangle will be black. Thus when cropping these types of images, you may want to disable this option.
Display and Caching Preferences