By default, Profound UI will mask a screen when a window is displayed on top of it. The color and opacity of this mask are configurable.
The "window mask color" setting allows for any valid color code to be used for the mask. Literals such as "black" or "blue" can be used as well as color hex codes.
The "window mask opacity" setting controls how much the masked screen bleeds through the masking color. Any value between 0 and 100 are valid. A setting of 0 would cause the mask to be invisible, while 100 would completely hide the masked screen.
Where do you save this configuration option? Here.