Hi all,
Just bought the game on steam and spent almost a whole day trying to figure this out and finally solved it. This is in regards to the problem of 'dark interiors' and 'rainbow/technicolor interiors'. Basically, it was a DirectX issue and I was using a Win7 - 64bit system with Direcx 11. I followed this youtube video (
http://www.youtube.com/watch?v=G1kqRDSKORI ) and reverted my drivers to Directx 9.0c and it fixed the problems and I can now play the game without and graphical problems.
Hope this helps and good luck. Don't forget to restart your computer after your done with making the changes.