# `Color.UnknownSortKeyError`

Raised when `Color.sort/2` is called with a `:by` value that is
neither a recognised preset atom nor a 1-arity function.

Has fields:

* `:key` — the unrecognised value.

* `:valid` — the list of supported preset atoms.

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*Consult [api-reference.md](api-reference.md) for complete listing*