Grant Morrison is as big a fan of Superman as anyone, but even he admitted in his book Super Gods that the clashing underwear is a stylistic error, something that goes to the idea of colourful strongmen performing feats. Take it off him, and his design becomes much more streamlined.
Batman's costume got away with it much better for decades, as it was black on grey so not much of a clash. But none of the modern movies have used it, so finally DC decided it wasn't necessary.
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"I'm not smart so much as I am not dumb." - Harlan Ellison
[quote]Grant Morrison is as big a fan of Superman as anyone, but even he admitted in his book Super Gods that the clashing underwear is a stylistic error, something that goes to the idea of colourful strongmen performing feats. Take it off him, and his design becomes much more streamlined.[/quotes]
More streamlined, and misses the point of the outfit (which he somewhat noted) being of a simpler time.
I'm okay with disagreeing with Morrison though.