adjust_vertex_colors.py

import bpy

obj = bpy.data.objects['sodark']
vcols = obj.data.vertex_colors
layer = vcols['Col']


def find_range(layer):
    lower = [1,1,1]
    higher = [0,0,0]
    
    for i in layer.data:
        col = i.color
        r, g, b = col.r, col.g, col.b
        if (r < lower[0] and g < lower[1] and b < lower[2]):
           lower = [r,g,b]
        if (r > higher[0] and g > higher[1] and b > higher[2]):
           higher = [r,g,b]
     
    return lower, higher

lower, higher = find_range(layer)

print(lower, higher)

layer2 = vcols.new('copy')
def adjust(layer, layer2, amp=2):
    for j, i in zip(layer.data, layer2.data):
        col = j.color
        i.color = col.r * amp, col.g * amp, col.b * amp

adjust(layer, layer2, amp=2)