Appearance of ice giants

With the Sudarsky classification scheme for gas planets, we sort of have an idea what they're supposed to look like at various temperatures and, consequently, locations in a solar system. What about the ice giants like Neptune and Uranus? The only two we've seen up close are well... blue. Would the appearance of ice giants at other temperatures be predictable by a Sudarsky-type classification scheme? Or do they all essentially look almost the same?

Does GJ 436 b look comparable to Uranus and Neptune? Or does its higher temperature affect its appearance?

Regarding GJ 436b, the red dwarf spectrum would affect its appearance too: if the colour is mainly determined by Rayleigh scattering then it may look pale grayish-blue, however there may also be factors such as absorption by methane to take into account.

Hmm, there's a few more questions I've about these worlds.

Is there an lower and upper limit for ice giant masses? I.e. what is the boundary between terrestrial planet and ice giant? What's the boundary between ice giant and gas planet? Or is it a rather hazy line?

How are their magnetic fields formed?

Are the compositions of Uranus and Neptune the result of the absorption of a lot of methane, ammonia, and water from the Kuiper Belt objects? And thus, would we expect a neptune-mass planet in a tight orbit, such as Gliese 436 b, to not have such a composition? Perhaps instead, resembling a mini-gas planet?

Presumably the lower limit is set by the planet's ability to accrete and retain a hydrogen atmosphere, so maybe a few Earth masses. There is likely to be an overlap in mass ranges between the smallest ice giants and the largest super-Earths.

As for the upper limit, who knows? HD 149026b has been described as a "super-Neptune", and it exceeds the mass of Saturn. Whether HD 149026b is actually an "ice giant" that formed in a similar way to Uranus and Neptune is another matter.

As for hot Neptunes, current theory is that they migrated in from beyond the ice line.

Alright, thank-you very much Lazarus.

Hi.

I would like to restart question.

Have we got today a sudarsky's like classification for ice giants?

http://en.wikipedia.org/wiki/Sudarsky_extrasolar_planet_classification

Seems that not much has changed if not feeling abandonned.

As for Ice Giants:
- Haze or no haze.
- What if it is a carbon-rich planet, would it be red like the outer asteroids?
Since organic compounds are not exposed to a sun that far out.
- Tholion-rich, like Titan. Yellow ice giants?

I had made a complex working planet type list.
I would not mind if we collaborate on it and make example images for it.
Maybe you might come up with a type I don't have.

The only hot neptune illustrated after a spectroscopical study is GJ436b. If this planet was a gaz giant, she would be blue deep, but they drew it brown, lay be because of carbon chemistry