Something like this?
There are couple of options.
If you just need a black character on a light background, then remove all lights in the scene
including IBL and set background to some bright color in Project settings.
If you want a character to have some specific color, then some more work be needed in addition to the above.
First, set ambient light to white.
Then remove eyes, teeth, occlusion and tear-line objects for simplification.
Apply attached skin to the character.
Select all materials and set a specific diffuse color.
Set background color.
For the case when character has hair, cloth, shoes, select all materials for the character, convert to Traditional shader, slide Self-Illumination to 100 and set a specific diffuse color.
Then remove textures from hair, cloth, shoes. You may leave opacity maps intact if needed (like for the hair).
