convert_white_to_black.py

from PIL import Image

img = Image.open("QQwhite.jpg")
width, height = img.size
result = Image.new('RGB', (width, height))

data = list(img.getdata())

for i, t in enumerate(data):
    if set(t) == {255}:
        data[i] = (0, 0, 0)

result.putdata(data)
result.show()