Can the Sudarsky's gas giant classification be applied to ice giants? Based on the temperature of a gas giant around another star, I have come to understand that it is possible to guestimate its appearance; a classification scheme for gas giants developed by David Sudarky.
I'm wondering if this scheme could plausibly be used to get an idea of what ice giants - Neptune and Uranus like planets - around other stars might look like? If not, are there any resources concerning this topic?
That classification scheme originates from before we had much in the way of observational data on exoplanetary atmospheres. It's not clear that it's a particularly useful description of how hot Jupiters behave: recent models, e.g. Gao et al. (2020) seem to indicate that silicate clouds and hydrocarbon haze are the main factors at play on hot Jupiters, rather than silicates versus alkali metal absorption.
As regards is applicability to ice giants, these planets have substantially higher atmospheric metallicities than gas giants, so it's not clear that these models would apply. For a study of some warm Neptune atmospheres, there's Fortney et al. (2020), who note that the cooling history of the planet is important, and things like tidal heating at depth caused by an eccentric orbit can have significant consequences. Or for a more experimental approach, see He et al. (2020), who indicate that hazes can form in hydrogen-rich atmospheres even in the absence of methane in the initial gas mix. It's a lot easier to find studies on hot and warm planets as these are the ones that are accessible to observations, so they attract more attention: habitable zone terrestrials are an exception to this pattern.
In summary, it's complicated, and things have moved on quite substantially since the Sudarsky et al. papers.