yesterday I painted the stone wall of Catelyns base. took some hours but i´m really satisfied how it turned out.
This is the palette (VMC) I used:
The trick in my opinion is a first lightness sketch of the wall, so that you have a zenithal light source (can be done via wet in wet sketch or AB) and then apply very thin layers of glazes to the single stones in different colors. So you get a natural variety of stone colors. This is how it looked after that steps:
After that every single stone needs to be shaded down (according to his
position on the wall, so upper stones least) and then pure white can be
used for highlights. To darken the recesses between the stones I used a
black wash I applied carefully only to the areas where needed.
this is a time consuming work, but well worth it in the end!