Try saying that fast. Anyway, here is the progress I have made and you can see that I changed the background color. It took a few tries to find a color dark enough to set off here colors while being light enough to see the lines of the drawing for the fins.
Believe it or not, I have made a good bit of headway since my last post; however, like the ocean takes centuries to reshape a continent one wave at a time, so too a painting. If you enlarge the image in my previous post and this one, you will see lost of subtle changes that take time and patience to achieve. Importantly, in the lower center, I have been working to make the brown stripes look more translucent. On the original picture they look almost like a thin wash that allows the underlying shell to come through. In addition there was another crack to try and replicate along with the fact that there are tons of lines, like tree rings, marking the growth of the shell to add in. I have only begun to capture all of the that. Lots of little effects to render the entire painting. For a while change will appear almost unnoticeable but it will be there if you look closely. Enjoy.