blender vertex paint function

vertexpaint.py

import bpy
from mathutils import Color

MODES = {
    '=': lambda a, b: b,
    '+': lambda a, b: a + b,
    '-': lambda a, b: a - b,
    '*': lambda a, b: Color((a.r * b.r, a.g * b.g, a.b * b.b)),
    '/': lambda a, b: Color((a.r / b.r, a.g / b.g, a.b / b.b)),
}

def paint(fn, mode='='):
    obj = bpy.context.active_object
    colors = obj.data.vertex_colors.active.data
    if not callable(fn) and not hasattr(fn, '__len__'):
        fn = (fn, fn, fn)
    for face_index, face_colors in enumerate(colors):
        if obj.data.faces[face_index].select:
            for attr in ('color1', 'color2', 'color3', 'color4'):
                i = Color(getattr(face_colors, attr))
                o = Color(fn(i) if callable(fn) else fn)
                setattr(face_colors, attr, MODES[mode](i, o))