Usage: saturation(amount)
This filter increases or decreases the image saturation.
amount
http://localhost:8888/unsafe/filters:saturation(40)/https%3A%2F%2Fgithub.com%2Fthumbor%2Fthumbor%2Fraw%2Fmaster%2Fexample.jpg
http://localhost:8888/unsafe/filters:saturation(-40)/https%3A%2F%2Fgithub.com%2Fthumbor%2Fthumbor%2Fraw%2Fmaster%2Fexample.jpg