Atmospheric effects - As mentioned before, I prefer it to be visually very similar to our atmosphere, with a few modifications. Some things I've considered:
- Atmospheric perspective, for starters; normally, our atmosphere 'retains' the blue light, literally making it a light-source in the day-time, and shifting the sun to yellow/red at the horizons. And at distance, objects increasingly shift in color towards the sky color. (Side note: Basically this has more to do with the Kelvin heat/light scale than the color of water or air; so other sky-colors aren't much of a possibility, barring dust and debris, at which point it’s not much of an ‘atmosphere’ any more.) If it were true to water, this effect would be vastly increased; in seawater at about 30 feet (I believe) all red/orange wavelengths are cut out, and at double that most of it is blue. The surface is typically pitch-dark. Blegh. Totally different story. So I want it to be transparent.
Water also has a fresnel effect at the surface due to surface tension and density differences; meaning that about half of the light is reflected off of the surface, with increased amounts the more oblique the angle becomes; this means that effectively, if you're looking straight up at the surface from underwater, you'll see through a rough circle with a vertical angle of about 40 degrees, but outside of that it'll reflect what's under the surface instead. This also sort of creates a fish-eye effect on the 'window' (so you actually see much more than 80 degrees out of your 'porthole'), and it cuts out the overall illumination very quickly.
Again, this is not really ideal... even considering it's a huge curved surface above. But I may still include a small surface-skin effect, justifying that at those altitudes, the difference in densities between semi-liquid and air is going to be very small. This might make a shimmery horizon effect in some situations; and with huge waves on top, a shimmery wave effect across the sky; both typically at dusk or dawn.
- I'd also like to know if stars and other extra-terrestrial objects are as visible; considering how many different densities of 'air' you're looking through. I want the stars to be visible; but maybe a flickery-wave effect might happen? Will it fuzz into bands and concentrations? Or will it mostly just diffuse?
You're asking for a transparent atmosphere. If you can find an element or compound that can be liquid and see-through, use that. Hydrogen peroxide might fit the bill, or at a lower temperature, like much lower, oxygen or nitrogen. But those end up more like white. It would be an extreme challenge to actually get it much more transparent than water.
Assuming that undefined liquid has similar qualities to water, but better:
The Fresnel effect will work with almost any liquid, though you can't see it through orange juice, so yeah, you won't see much outside the atmosphere. Heavenly bodies are gonna be a no, unless you find something as transparent as aforementioned, i.e, more clear than water. The 'shimmery effect' will be ongoing at all times, because waves and such.
If you can see any heavenly bodies, then yes, you will find that they diffuse along the surface. But note: you haven't said what kind of liquid, probably on purpose, and thus my answer is almost as hypothetical as your question.
Assuming you find a water-like liquid of a higher transparency.
This would be all but invisible. Almost totally undetectable. From off the planet, you would see a bunch of whatever lives there 'flying' close to or far above a relatively small, sandy/rocky core. And also some weird looking volcanoes, if you have any. Everything would get very ethereal.
Side note: you'll have to make the core pretty dense to hold a liquid on top like that.