A transparent red mask will cover the entire image, except the area previously selected with the Lasso. A screen shot is shown at left. Click on the Paint Brush tool. Now we'll paint out the mask with black, white or shades of gray, which are the only colors available in Mask mode. A foreground color of black will be selected automatically in the Color Palette on the right side of the work space.
Black paint adds to the red mask, while white paint removes it.
You can also remove the red mask by clicking on the Eraser in the Attributes toolbar to erase parts of the mask you've painted back in. However, you cannot erase the initial red mask created by the Lasso selection tool. Mask Mode lets you toggle back and forth, adding and subtracting to the mask by changing from black to white paint color. Use the Color Palette to select paint color, or click in the Attributes toolbar's color box to access colors. That way you'll be able to see image detail better while painting.