As far as I know all that is required for the mini's is that the bitmap be 36x36 with a black background and the ship 'front' needs to be pointing upwards. The Game takes this and does the different 'rotations' as needed.
The one I made is 'exactly' the one you posted with the teal background color. I changed the teal to black and did a bit of 'tweaking' with the contrast, sharpness and gave it a tiny bit of shading. I also kind of cheated and added engine glow which I don't think the stock ships have or use.
Attached to this post is the .bmp Version. Rename the file and try it in the game. Let me know how it looks.
Cheers!
