Welcome to the forum.
Is there any way that you could post a short excerpt from that footage, so that others could see it, and experiement with it?
One of the issues with underwater footage, or photography without flash, is that the deeper one goes, the less complete the light specturm is - not just a color balance, or cast, but a diminished spectrum. That can create some issues when it come to CC (Color Correction).
As an experiment I went for another dive today, this time taking the same camera (Canon S110 with underwater white balance mode active) as well as a GoPro with a red filter. The video from the GoPro seems to have much more colour in it so I think it's a case of the Canon not capturing as much of that spectrum. I'll do another dive tomorrow and manually set the white balance to see if it makes any difference. I'm so use to shooting on the GoPro that I was surprised by the reduced colour in the Canon.
Is there any way to determine how much of red / green / blue is available in the video using PE11 ?
Thanks for the reply.