Hi there guys. I hope you can give me a hint on this one:

I have a scene with different walls. Each wall has different textures (as jpeg) loaded on the materials->diffuse (mia material_x_passes).

The problem: All the darker/grey textures I load into the materials are not affected by light (at all) Why is that so? - In the render all textures interact correctly with the direct lights and photons except for the materials with dark textures.
What am I doing wrong here?

Using maya 2015