Colour Mapping on Tilting Surface

Hi Everybody. 

I am trying to make louvres which will be painted a different colour on the inside compared to the outside. The problem I am facing is that as I have a tilting louvre facade, at some point, the surface on the inside is tilted towards the outside (please see images attached). So the colour 'green' needs to be painted only externally, once the louvre is flipped beyond a certain angle, its face at the back should be painted.

I was thinking maybe one could 'project colour onto the one side of the facade??

Could anybody help or give ideas on how I could achieve this?

Kind Regards

Frederich