code: def vertex_to_face_color(vertex_colors, faces):
      
      vertex_colors = to_rgba(vertex_colors)
      face_colors = vertex_colors[faces].mean(axis=1)
      return face_colors.astype(np.uint8)
docs: Convert a list of vertex colors to face colors.
  
      Parameters
      ----------
      vertex_colors: (n,(3,4)),  colors
      faces:         (m,3) int, face indexes
  
      Returns
      -----------
      face_colors: (m,4) colors