You need to do two things:
- Put the color you want of your material into the Emissive slot in the output function
- Mark the material as “Unlit”
You have to do this for each material. (It is possible to write code to do this for you, given some assumptions, for an entire level, but that’s beyond the scope of a forum post like this!)
Finally, I don’t think you will get the result you want by doing this. It turns out that lighting/shading is important to our perception of the shape of objects. Shadows are also important to our sense of object location. Making everything uniformly lit from all directions without shadowing (which is what Unlit does) will actually make everything blend together, and will make your game look like a bad '90s 3D game.