By default, the mask overlay displays red semi-transparent pixels to show the mask on the image. If a different color or opacity would make the overlay easier to see on an image, change the color or opacity for the mask layer.
To change the mask overlay color and opacity:
On the Layer palette, double-click the mask layer button, right-click the mask layer button and choose Properties, or choose Layers > Properties to open the Layer Properties dialog.
Click the Overlay tab and change the following:
Overlay Color The default overlay color is pure red (RGB 255, 0, 0). Click the color box and choose a new color.
Opacity The opacity of the overlay. The default is 50 percent.
Click OK.
Creating Gradient, Pattern or Texture Masks