I was thinking of an alien humanoid charcter for my super powered beings story that would be completely black and faceless with similarities to venom and its strings of symbiotic goo but this character would not be a symbiotic life form.
I thought that the rainbow colours seen on oil spills on puddles especially on bumpy black tarmac look beautiful and almost sinister at the same time (maybe its the rainbow colours on black or the flammable danger factor) and that this effect would look good on the aliens skin.
I was told that it doesn't have to be water with a thin film of oil that can create these colours as the light reflects from both above and below the oil layer but any polar solvent can be used instead of water (if this is incorrect can anyone name a suitable substance instead please)
I thought that the alien could sweat or secrete both the polar solvent and oil from its black textured skin and be covered or at times only parts of its body will have the rainbow light effect.
So my question is which polar solvent or any other substance would make an interesting base for the oil to create its rainbow pattern and could also itself serve as a weapon or have other useful properties that would be much better than water?
At first I thought Acetic acid or Formic acid could be interesting as they could be used as mild weapons themselves, I believe theres an ant that stings with formic acid, although very mild in terms of super powers in high concentrations this could be an effective weapon if spat out.
As this is an early stage of character design i still need to design its home planet and some of its abilities but with an idea of what solvent it secretes will help with those aspects of this character.
EDIT: the question was more about the properties of polar solvents and which have the most interesting chemical qualities that could be tweaked into a superpower either in combination with the oil burning like ethanal or a differnet effect entirley of its own. i added the word substances to the title as i was unsure if other liquids could work the same as water.