The Opacity slider controls the overall transparency of the surface. If you load a colored image, Enscape will automatically convert it to black and white, so you don’t have to worry about that.
Grey areas will appear partially transparent, such as glass. It refers to the Opacity value, so a black area (which equals zero) on the image used will result in a perfectly transparent portion of the surface, while a white area will appear perfectly opaque. The Texture parameter allows you to control the transparency using a 2D image, a map.
