All (AFAIK) vanilla overworld/nether biomes have their sky colour assigned with this private static method, so exposing it would be useful for modded biomes. (It takes the biome temperature and calculates a sky colour from it.)

Here's another addition that'd benefit from global AW.

It's now called OverworldBiomeCreator.getSkyColor in 1.19.3 and it's protected. Is that good enough?
EDIT: not good enough, no