I deleted all the lights in my scene. However even without light some of my textures are uniformily "lighted up", or at least visibleas you can see on the picture. The visible textures are psd files I put via texture nodes. This makes my textures very flat looking. Any idea what causes this and how to get rid of it?
The problem is thts you connected the Textures directly to the Mix Shader Node.
To fix the problem you should add a BSDF Node between: the texture Node connects to the BSDf's color socket and the BSDF connects to the mix node.
I would use the principled BSDF but you can use any one.