That's complete nonsense, though obviously not 100% (I'm no sommelier) I could definitely identify some grapes blind (and then implicitly could tell you if it's

That's complete nonsense, though obviously not 100% (I'm no sommelier) I could definitely identify some grapes blind (and then implicitly could tell you if it's red or white). And a master sommelier... well they can do that and then some. If I wasn't sure of the grape, sure I might not confidently say if it's red or white. Because other than visually that isn't really as big a deal as it naïvely seems? Wine doesn't taste 'red' or 'white' it has different flavours and some grapes are red and others are white, but that's really only a visual difference. (Ok fine some flavours or textures are so much more common in one vs the other that it might allow a solid guess of the colour even if you had no idea of the grape - 'minerally' or 'bready'/'yeasty' tasting/smelling is probably white; very tannic is probably red. But I think my point stands, it's pretty meaningless, and certainty will come from identifying something more specific, and then knowing what colour that is, to satisfy the naïve hater that thinks that's the most important trait.)