You can use any kind of procedural or image-based material as a light gel.

Here's a simple example using an IBL region transmap image. Having made your image, you can scale and position it using the UV scale and offset dials.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)