Color mask by scene materials

To quickly create a color mask by materials, assigned to the scene objects, for post-processing

you can use the following script:

import bpy
import random

for material in bpy.data.materials:
    material.diffuse_color[0] = random.uniform(0, 1)
    material.diffuse_color[1] = random.uniform(0, 1)
    material.diffuse_color[2] = random.uniform(0, 1)

import bpy

import random

for material in bpy.data.materials:

material.diffuse_color[0] = random.uniform(0, 1)

material.diffuse_color[1] = random.uniform(0, 1)

material.diffuse_color[2] = random.uniform(0, 1)

This script assigns each material its own random viewport color.

After assigning colors, you can render the viewport by selecting in the 3D Viewport menu: View – Viewport Render Image (Viewport Render Animation), and save the resulting image for later use as a mask in compositing.