How do I go about changing the saturation of an image using PIL or Pillow? Preferably I'd like to be able to use the solution together with the django-imagekit package. The reason I need to change the saturation is to create an effect where when the user hovers a black-and-white image it turns to colored.
If you're using django-imagekit, you can just use the bundled Adjust processor:
from imagekit.processors import Adjust
Adjust(color=0.5)
Under the hood, this will do exactly what @abarnert recommended.