Mesh.colors returns zero

I have this simple script. I tried to put it on simple mesh and cubes but mesh.colors is always zero.
What am I missing here?

Mesh mesh = GetComponent<MeshFilter>().mesh;

This is the shader i am using

    Shader "Custom/Vertex Colored" {
    		ColorMaterial AmbientAndDiffuse

Well, if mesh.colors32 / mesh.colors return an empty array that means your mesh doesn’t have any vertex colors.

As you can see as example the Unity default cube mesh doesn’t have any vertex colors, only vertex positions (verts), and two sets of UV texture coordinates