Desaturation
Generally, I find whenever something is stylistically heightened to the point where it’s difficult to take seriously, ditching the color immediately improves my suspension of disbelief. There are, I think, two aspects to this. One is that a black-and-white world is clearly not reality; this is an idealized, simplified dream world, that must be taken on its thematic strengths rather than its plausibility. The other aspect is that a loss of color helps to blur the edges. When everything is reduced to light and shadow, CG no longer looks so false. Wonky sets and costumes are easier to take at face value.
Basically, black-and-white strips away the distraction of an expectation of realism. Which in most cases, to my mind, can only be a benefit to storytelling.
Now don’t get me started on sound…