Make all materials in Blender (2.79) be influenced by vertex color.

apicula_material_vertex_color.py

import bpy

for mat in bpy.data.materials:
    mat.use_nodes = True
    
    out_node = mat.node_tree.nodes[0]

    mat_node = mat.node_tree.nodes[1]
    mat_node.location = -140, 425
    mat_node.material = bpy.data.materials[mat.name]
    
    geom_node = mat.node_tree.nodes.new('ShaderNodeGeometry')
    geom_node.location = -140, -5

    mix_node = mat.node_tree.nodes.new('ShaderNodeMixRGB')
    mix_node.location = 95, 256
    mix_node.blend_type = 'MULTIPLY'
    mix_node.inputs[0].default_value = 1.0

    mat.node_tree.links.new(mat_node.outputs['Color'], mix_node.inputs['Color1'])
    mat.node_tree.links.new(geom_node.outputs['Vertex Color'], mix_node.inputs['Color2'] )
    mat.node_tree.links.new(mix_node.outputs['Color'], out_node.inputs['Color'] )
    mat.node_tree.links.new(mat_node.outputs['Alpha'], out_node.inputs['Alpha'] )