You can adjust the white balance in lightroom pretty easily and may get some improved images. This is works best if the shots were made in no more than 20 feet of water with lots of natural light. Beyond that, you really should start looking at add a single strobe. A Backscatter MF 1 or 2, or an Inon 220 might be your best entry level options.
Thanks! Looks like I can post images now, so why not?
From my last dive in before I broke my leg in September. Hope to be diving again in January.
Egg Yolk Jellyfish in Puget Sound: