Old Photoshop from that era defaults to a single RGB layer. To turn it into an RGBA layer (e.g. for drawing objects with a transparent background) you need to rename the layer. Not very intuitive but Photoshop users learned to do it. In early Gimp 0.x releases how do you turn the initial single RGB layer into an RGBA layer? You rename it. This is not a coincidence.
In contrast in mspaint there are no layers, there is no RGBA mode.
