With Rhino Render the insides are black because there is no light inside them, not even after clipping as clipping is only a visual change, not an actual geometric change. It doesn’t look like clipping fill surfaces are being pushed to the renderer yet - those would cover the black areas and shade as regular surfaces.
Thanks, makes sense. there used to be an option to ‘cap’ sectional cuts I think (it’s mentioned on a previous post I found somewhere where they flagged the same issue I am ) and I suppose I was just hoping there may be a tick box option somewhere - in the end I just did a sacrificial Boolean cut on a duplicated version of the same building and used that for the visual/render