Polygon Lighting?

Hello,
I have a procedurally created mesh as in the picture, it has the standard diffuse shader.

What should I do to achieve something like this? Should I re-calculate the surface normals?
Any advice, tip or keyword to search is appreciated. Thanks in advance.

 

First of all, if you look at those triangles you will notice the entire triangle has the same color, so it means that each triangle will need to have hard edges towards all it's sides, otherwise the gpu will interpolate and smooth it out.
For the colors my guess is that the image you show is painted, but in your case I would suggest vertex colors.

 

Thanks a lot, your answer led me to this page and the issue is solved.
http://answers.unity3d.com/questions/781470/change-mesh-color-with-shader-or-meshcolors.html