Create game without using textures

Hello,

I wish to make some levels in a game without using textures, but only models and shaders.

See this text I created just to highlight my problem:




As you can see, even if I used a toon like shader (Team Fortress 2) the surfaces are really too flat, plane models have no detail.
Obviously that is a simple example just to highlight the problem.

I wanted to find a way to "fill" the flat area (planes) with "something" like a light reflection, or a kind of "noise" to make it more various.

I'm not a designer so I cannot explain in detail the concept, but I hope you understood what I said.
I was even thinking to a shader to get a pencil-like or a sketch like effect, like if the plain surface (the blue surface for example) does not appear as uniform, but with a kind of "noise", like a pencil that fill a surface.
Is it possible? Can you help me?
I like toon style that could fit in this technique, but I accept anything, suggestion, shader or more.

Thank you for your help!!