The RGBA-Mask are the bitmasks used to extract that color from a pixel. It is used to e.g. define the background of a newly created Surface. Using zeros for the RGB-Masks sets a default value, based on the depth But using zero for the Aalpha-Mask results in an Alpha-Mask of 0. By default Surfaces with an Alpha-Mask are set up for blending. You can change the blend mode with Surface.setBlendMode.