Purple elephant.

"She is like the *purple elephant".

Does anyone knows why it is considered as a compliment?
then he says she has a wonderful personality.

Thanks a lot

Hard to say without more context, but there is a common remark about "the elephant in the room," something it is impossible to ignore. A purple elephant, in this context might mean someone so larger-than-life, so unusual, that one cannot possibly ignore it. Or her.

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