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How do you assign a random vertex color in Blender?

Published in Blender Vertex Colors 5 mins read

Assigning random colors to vertices in Blender can be achieved through several methods, including using the "Random Flow" addon (as hinted in the reference) or scripting. Here's how you can do it:

Using the Random Flow Addon

While the provided reference mentions "Random Flow," it doesn't detail the exact steps. However, here's a general idea of how an addon like "Random Flow" (or similar addons focusing on procedural generation) might facilitate this process. Note: The exact steps may vary depending on the specific addon.

  1. Install the Addon: Download and install the "Random Flow" addon (if available) or a similar addon that offers vertex color manipulation features in Blender. Usually, this involves going to Edit > Preferences > Add-ons, and then installing the downloaded .zip file.
  2. Enable the Addon: After installation, enable the addon in the Add-ons preferences.
  3. Select the Object: Select the object you want to apply random vertex colors to in the 3D viewport.
  4. Access the Addon's Functionality: The addon will typically add a panel or operator in the 3D Viewport's sidebar (usually accessed by pressing 'N'). Look for options related to vertex colors or randomization.
  5. Apply Random Colors: The addon should provide a function to assign random colors to selected vertices or all vertices of the object. You might have options to control the color range or distribution. Follow the addon's specific instructions to execute this function.
  6. View the Results: Ensure you are in Material Preview or Rendered view to see the vertex colors. You might also need to create a material that uses the vertex color data.

Using Python Scripting

A more direct method involves using Python scripting within Blender. Here's an example:

  1. Open the Scripting Tab: Go to the "Scripting" tab in Blender.

  2. Create a New Script: Click "New" to create a new text data block for your script.

  3. Write the Script: Paste the following Python script into the text editor:

import bpy
import random

def assign_random_vertex_colors(object):
    """Assigns random colors to the vertices of the given object."""

    mesh = object.data
    if not mesh.vertex_colors:
        mesh.vertex_colors.new()

    color_layer = mesh.vertex_colors.active

    for poly in mesh.polygons:
        for loop_index in poly.loop_indices:
            r = random.random()
            g = random.random()
            b = random.random()
            a = 1.0  # Alpha (transparency), set to 1 for fully opaque

            color_layer.data[loop_index].color = (r, g, b, a)


# Get the active object
obj = bpy.context.active_object

# Check if an object is selected
if obj is not None and obj.type == 'MESH':
    assign_random_vertex_colors(obj)
else:
    print("Please select a mesh object.")

#Update the mesh
obj.data.update()

  1. Run the Script: Press Alt+P to execute the script.

  2. See the Result: To visualize the vertex colors, you'll need to create or modify a material that uses vertex color data. In the Shader Editor, add an "Attribute" node, type "Col" (or the name of your vertex color layer if you created one) in the name field, and connect its "Color" output to the "Base Color" input of your Principled BSDF shader (or any other shader). Also, switch to Material Preview or Rendered view in the viewport.

Explanation of the Script:

  • import bpy: Imports the Blender Python module.
  • import random: Imports the Python random module.
  • assign_random_vertex_colors(object): This function takes a Blender object as input.
  • mesh = object.data: Gets the mesh data from the object.
  • if not mesh.vertex_colors:: Checks if the mesh has vertex color layers. If not, it creates a new one.
  • color_layer = mesh.vertex_colors.active: Gets the active vertex color layer.
  • for poly in mesh.polygons:: Iterates over each polygon in the mesh.
  • for loop_index in poly.loop_indices:: Iterates over each vertex in the polygon (using loop indices).
  • r = random.random(), g = random.random(), b = random.random(): Generates random red, green, and blue values between 0 and 1.
  • color_layer.data[loop_index].color = (r, g, b, a): Assigns the random color to the vertex in the active vertex color layer.
  • obj = bpy.context.active_object: Gets the currently selected object.
  • The rest of the script checks if an object is selected, ensures it's a mesh, and calls the function to assign random vertex colors.

Important Notes:

  • Make sure you have a mesh object selected in the 3D Viewport when running the script.
  • If you already have vertex color layers, the script will use the active one. If not, it will create a new one called "Col".
  • The script assigns random colors to each vertex. If you want different randomization behavior, you'll need to modify the script accordingly. For example, you might want to assign the same random color to all vertices of a face.
  • The script updates the mesh in the last line, ensuring that the changes are visible in the Blender interface.

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