The skull is starting to take on more depth and I am getting quite happy with the horns and the back portion of the wall but as much as I love the top portion of the wall and it looked good in the reference photo it is just much too dark and does not seem to 'fit in'.
So I have decided to lighten it and rather replace it with a sky rather than a dark shadow on the wall as in the reference photo. Kind of wishing I had used non-staining pigments now....oops! The blue I used is indandathrene blue which is a heavily staining pigment which I applied quite heavily. It will be interesting to see how well it can be removed and to what extent without damaging the paper, hmm :)