I created 2 pictures using 3D View.

1/ 'High quality'
http://www.mediafire.com/i/?6vi1x12jwccvdpv
The room appears very dark and the walls transparent.
Is this normal ?

2/ 'Fast create'
http://www.mediafire.com/i/?dedjix8aqhw6n3s
In this case 2 walls defined with the same color code appear as light brown or dark brown. The difference in shading is according to me much too big.

Am I doing something wrong, might I have misunderstood something ?