Can you post some screen grabs of the variations? It would prove difficult if the changes are linear and not a sudden switch as you would have to keyframe the corrections over time to match the change over time produced by the camera. That doesn’t sound fun 🙁
If the change is a sudden switch, take each event/clip and choose which one you want to be your standard. Get it to look how you want and then move on to the second one. Color Corrector and Secondary Color Corrector are your friends. Also Curves can help a lot. Make sure the white balance is set properly to match in each event before adjusting too much. This at least will give you a better opportunity at starting on common ground.
Some other options:
1. Reshoot.
2. Apply some filters to make it look like it was on purpose if that is even possible.
3. Chalk it up to experience and refund the client if there is no way to make it look how it should.
j razz
https://www.jrazzcreations.com