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In large quantities, water appears blue. As our oceans are made of water, they too are blue.

My question is simple what potential thalassogens would not appear blue if they formed the seas of an alien planet? Stuff that's blue but not water-blue, like some interesting shade of blue, will also be accepted.

A couple of requirements:

• The chemical must have a liquidity temperature range which is also habitable for life - so no molten tungsten please.


• Ideally, it should be at least a potential solvent for alien life of some kind.

EDIT: I've altered the question to make it less opinion based. What elements/compounds fulfill the bullets above and would appear

-Purple

-Green

-Orange

When in large liquid bodies?

Ammonia has a tendency to dissolve alkaline metals. This answer claims this would make the oceans very blue, this page suggests brown. The argument for blue is that solvated electrons make solutions deep blue; when the concentration is high ($[H]>3$M) the colour goes copper, which might be the source for the brown. Now,

Liquid nitrogen, helium and hydrogen are pretty colourless, but liquid oxygen is sky-blue (and under pressure and low temperature forms a lot of colourful crystal phases). Ozone is darker blue. Hydrogen perioxide is apparently a watery transparent blue. Of course, a planet with liquid oxidant oceans may have some habitability issues. I suspect that the same dispersion effects that make water blue will make liquid nitrogen, helium and hydrogen oceans look blueish.

Hydrocarbon have plenty of opportunities to acquire colour. Liquid methane is again colorless, and might look very clear on worlds like Titan where atmospheric methane has already filtered out the wavelengths that tend to be absorbed. However, the atmospheric haze consisting of photochemical smog is clearly yellowish and likely soluble in the methane. I would expect most hydrocarbon ocean planets to have oceans coloured by more complex tholin molecules, that would tend towards the red-yellow side. In extreme cases, maybe black.

Sulphuric acid is again colorless, but does tend to turn yellowish when contaminated with iron ions. And again organic matter and other substances can make it yellow, red, or black.

Red Algae

The easiest way to get a non-green/blue ocean is perhaps to use a life form. Just make sure your ocean has the ideal nutrients for them.

Salt Lake in Turkey Turns Red Because of Algae Bloom

https://abcnews.go.com/International/salt-lake-turkey-turns-red-algae-bloom/story?id=32590572

Water isn't blue. Or not very. Water appears blue-ish because most of the light you are seeing is reflected sky. It's not the same blue, because much of it is absorbed instead, so you are in effect getting dimmed skylight, or light blue mixed with black.

Water can be coloured by what's in it. Suspended clay gives it a brown colour. Dissolved tannic acid (peat bogs) along with micron sized peat particles make it the colour of strong tea in your cup, black if more than a foot deep.

With algae in it water is green. There can be a substantial difference in green depending on which algae. Some algae are red -- hence red tide.

Runoff water from a glacier is often a milky gray initially. As it gets far enough and slow enough for larger rock flour particles to settle, it takes on a blue cast. The particles that remain are are close in size to the wave length of blue light, so it's scattered more.

So now you have several mechanisms to colour water:

• Suspended solids


• Dissolved solids


• Micro-organisms.


• Sky reflections.

There is no reason for any of these to not work with other liquids.