personally I find those colours absolutely awesome! I'll definitely try experimenting with a grey card next time out but, as you probably know, I'm actually really happy with the MWB on my GH5 (red filter/grey translucent plastic). Using ambient light like in your video gives everything a much more natural feel, IMHO, plus you avoid having to deal with backscatter and annoying the marine life with thousands of lumens in their eyes. At around 2'50" you were filming inside the wreck, and I'm pretty sure the GH5 wouldn't have handled that anything like as well.
Very nice video!