The apparent color of water surfaces is fascinating, and much more complex than I realised (a combination of reflected light, refracted-and-transmitted light, absorption by vibrating H2O molecules, internal reflection by suspended particles, internal absorption by suspended particles, blue-shifting by vibrating-and-re-emitting H2O, ... etc).
But one thing I can't seem to find clear info on is the effects of polarization on color.
e.g. in this answer https://physics.stackexchange.com/a/423122/244448 :
"When light glances off a smooth surface, the surface reflects light with horizontal polarization more effectively than light with vertical polarization (see Brewster's Angle), so some skylight can end up darkened - or brightened - relative to other colors depending on the angle of polarization and the angle of incidence."
The key phrase: "darkened - or brightened - relative to other colors depending on the angle of polarization" is tantalising - experimentally, sometimes water surfaces appear darker than the sky, and sometimes they appear brighter, and there's no obvious pattern. But if the above quote is correct, and polarization both darkens and lightens colors, then polarization (which I cannot innately detect/see) could fully explain that.
NB: one of the problems I've encountered in exploring this is that - of course - most photographs of water are "fake" without recording this: in general, all photographers use polarizing lenses to some extent, from the universal sky-filters to the slightly more specialist rotating paired polarizing lenses on SLRs. This is not something that occured to me until I started digging in to polarization. This info doesn't (usually) appear in photo metadata, since it's outside the camera's electronic system.
(i.e. I'm finding that the only way I can investigate this phenomena is to physically travel to locations and bodies of water at times of day and weather conditions, which is severely limited by budget!)