Color

Weight

Roughness

Backlight

 

Fresnel affects Diffuse

Direct Diffuse

Indirect Diffuse

 

Surface normal direction

When rendering diffuse surfaces it is very important that the normals of the geometry face in the right direction. In the example below you can see the difference between normals that are facing inwards in the wrong direction (left side) versus those that are facing correctly in the outwards direction (right side).