pix = (255,100,0)
print pix
(255, 100, 0)


print type(pix)
<type 'tuple'>


pix[0] = 150
Traceback (most recent call last):
  File "C:\Users\Susan\AppData\Local\Enthought\Canopy\User\lib\site-packages\IPython\core\interactiveshell.py", line 2883, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-5-7ee07c725449>", line 1, in <module>
    pix[0] = 150
TypeError: 'tuple' object does not support item assignment

npx = (255-pix[0], 255-pix[1], 255-pix[2])
print npx
(0, 155, 255)