Check the Zone for a Virus savestate made close to the stated spec. The two existing copper lists moved to $68800 and a third one added which is common to the first two. The third one controls the colors and the line where the change is made. The bands are 10 pixels wide and that isn't even enough. The palette was constructed by loading IFF of main picture into Personal Paint, decrease brightness 11% 8 times. The main 16 colors were stripped out of the copper list each time the stitched together to make one big one for the Virus program.
I think if the color change lines moved down one pixel for each pixel the ship gained in height, it might look better. More bands might be better. The gradient might look better if done by hand. Maybe the bands shouldn't be equidistant. Whew! already too much work for me. Set WinUAE for A500 512K KS1.3 and load the savestate for some laughs.