Those are two very different shades of purple dude, and I really would say the Nomura sketch is actually a dark blue (though it's most likely an accent shading color and his outfit is meant to be black) but I already said Terra, Locke and Celes are different but just about everyone else is a pretty good interpretation. Also Locke is not wearing a bowler hat, its just a more intricate bandana (almost a turban) that covers his whole head where as the sprite has a simple blue one wrapped around his head. As for Bartz looking feminine, that's just Amano's style. If the guy doesn't have facial hair, he's usually very feminine looking. But here's a comparison from sprite, Nomura's chibi transcription, and Amano's original work.
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I don't think the jump is really that drastic here. Color is off sometimes but we're talking about technology limitations at that point. This isn't like FFV where the Amano art is way off from the sprite art. Detail is lost but one look at Nomura's design of Cloud vs. his sprite and you'll notice a lot is missing as well but the distinguishable characteristics are still there. It's not until FFVIII and the PS2 FFs that we begin to see clear across the board translations of the characters and even that doesn't stop the developers from cheating, like how FFX makes sure that you rarely see Lulu's full character model in cutscenes and CGI sequences, cause the team couldn't be arsed to animate her belt skirt so many times.