How do I turn a scene into a 3-color...logo or cartoon looking image? I want to turn a scene into a more graphic-design looking image, something that can be screen printed onto a T-shirt which means few colors. Is there a conventional way to do that which makes the rendered models look crisp and very monotone, but still take into account a little bit of shading? 

More like these examples but with a crisp distinction between colors instead of a smooth gradient https://www.google.com/search?biw=1600&amp;bih=757&amp;tbm=isch&amp;sa=1&amp;ei=04mGXZK4KsGOtQWH9ab4DA&amp;q=shaded+logos&amp;oq=shaded+logos&amp;gs_l=img.3..0.17866.18966..19014...0.0..1.222.1149.9j1j1......0....1..gws-wiz-img.......0i67j0i8i30j0i24.px0-LbngAZk&amp;ved=0ahUKEwjS7cmk4uLkAhVBR60KHYe6Cc8Q4dUDCAc&amp;uact=5

I am sure there is a way to set that up, but I am not sure what kind of lighting and materials would accomplish this.
Oh...you want to do that to a scene? Whoops. Well this is how it would work. You would still use nodes, but instead of using the Material nodes, use the Compositing Nodes (the tab with the two pictures at the bottom of the Node Editor.)

This is what the scene would normally look like.


Here's a few different effects you could try out.

A Persona-esque effect:


A Noir (or Gameboy) effect:


Or just a totally simplified color scheme:


Again:
Make sure your film is transparent. Open the tab with a photo camera on it in Properties, scroll down to "Film," and check the transparency box.

Feel free to mess around with the ColorRamps until you get a good result. Any change makes a big difference! Just remember to keep it on "Constant."