Animal mutated with truer colouring (11)

I believe the answer is:

ultramarine

'colouring' is the definition.
(ultramarine is a kind of colouring)

'animal mutated with truer' is the wordplay.
'mutated with' indicates an anagram.
'animal' anagrammed with 'truer' can make 'ULTRAMARINE'.

(Other definitions for ultramarine that I've seen before include "Brilliant deep blue" , "Vivid blue" , "Blue pigment originally made from lapis lazuli" , "See a colour" , "Tone" .)

I've seen this clue in The Times.

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