EZUWA 500' GoPro

[Aquaventure]

Yes, you can effectively adjust still files digitally (especially RAW format) but it is best to shoot the highest quality video (and stills for that matter) from the start.  The less you need to edit or adjust the better.  Especially HD video files.  Unlike a still RAW file that can be adjusted a great deal without any image degradation, HD video files are shot in a highly compressed format.  They can be altered a bit however, the alteration degrades the file.  This varies from software to software.

When shooting HD video (especially underwater) it is critical to have the proper or as close to proper White Balance, exposure, etc.  Green water and blue water filters are a huge asset in assisting in this process, especially in video cameras that do not allow manual White Balance settings.  Yes, filters do filter out a small amount of light however, the video camera's metering system (GoPro's or any automatic video camera) automatically adjusts for optimum exposure.  Filters will also do amazing things for contrast (especially in cloudy green water).  If this type of correction is attempted in post production, the file may have significant noise added to it.  Especially in darker conditions.

I hope this helps