But I disagree that post-apoc world has to be grey and colorless. Humans like color - I suspect they'd find a way to inject into the environment in some way or another. Movies/media have used the same post-apoc like setting for years - it wouldn't hurt to stretch the imagination and think of something different.
But then it "wouldn't be fallout."
I'm not saying there should be crtoony rainbows, white unicorns and purple cotton trees everywhere ... but a red sweater worn in a rocky desert under even the darkest, stormiest skies will still be red. There could at least be some overgrowing green foliage all about these ruined towns to break up the monotony...
In fact, it should mostly be overgrown green foliage, if anything. (Except in the dessert, I suppose)