The first two Fallout games made logical sense for their setting to be arid, dusty, and bleak. It was just a few decades after nuclear armageddon, as well as being set in the southern California/Nevada part of the western US, which is already dry in non-irradiated conditions. I could even buy Fallout 3 being a choked-off mess since the US capital would have been hit especially hard by nukes. And of course New Vegas is set in the middle of the Mojave desert.

There was no reason for Fallout 4, or really any other future game, to be so dry and brown. We know for a fact that plant and animal life returns relatively quickly after major nuclear detonations and leaks. Yes, there is an increased presence in certain diseases and poisoning in the environment, and it's certainly not safe for people to live long healthy lives for quite a while. But nowhere on Earth has a large influx of radiation turned the land into a blighted hellscape. Places like the Commonwealth should be completely overgrown and consumed by nature. Sure, have mutated bugs and yao guai prowling through the forests. But the time of dead sparse trees and dusty empty wilderness is done... unless you set the game in an area that's explicitly desert. (Thank God for the Regrowth overhaul mod. It does everything I want in Fallout 4!)

Unfortunately, I think the brown color palette and bleak open world are just features of Fallout by this point. Alongside the Brotherhood of Steel, super mutants, and cheery 1940s/50s music that uses nuclear bomb metaphors for sex.