Update - 8 Byte Method verified
I've written a quick tool to the job for me... unuseable by anyone else, but it has helped me figure out that my methods for the exact color calculation are wrong. I still do not know how the color is calculated right.
But I've made a cross-examination. The colors do not match at any rate, however the shapes of both images (original and converted) match up with each other, so the decoding process seems to be correct.
It seem I was right, when I said all we had left was to find out the color calculation process. Oh, I love it when I'm right.