Like a cowardy custard? (6)

I believe the answer is:

yellow

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'like' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I don't see?

I can't explain the remainder of the clue.

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(Other definitions for yellow that I've seen before include "egg-hearted perhaps" , "Colour of egg yolk and cowardice" , "Coldplay song; colour" , "Primrose-coloured" , "Daffodil colour" .)

I've seen this clue in The Guardian.

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