When Supes wakes up, he will find himself in the new DC perkiverse, where even Batman smiles and cracks jokes. He will naturally follow suit. But there should be a period of transition from death to the new normal, and the black costume would make that more dramatically effective.
Clothes don't create drama. Writing and acting create drama. Just because the comic did something a certain way, that doesn't mean it's the only way it can work. The whole problem with Zack Snyder's films is that he's better at slavishly copying other people's work than he is at coming up with his own stories.
A lot of words considering you have no insider knowledge of these specific projects.
And why should those projects be exceptions to the industry-wide pattern? The only times that writers have any power in Hollywood features is when they're also directing or producing the films they write.
We do know that Nolan and Goyer went to WB with their idea for Man of Steel, Nolan was made producer of the project, he offered it to several directors until Snyder accepted and signed on to directed a script by Goyer and Nolan. This does not match with your idea of Snyder as some sort of demented supremo.
Actually MoS was the better of the two films by far. It would've been quite good if the third act hadn't degenerated into endless disaster porn. But JL most likely has more in common with BvS than it does with MoS, because MoS had Nolan's involvement and was made before the WB execs started pushing for its big crossover universe.