Plant used for colour, as a Welshman would say (7)

I believe the answer is:

dyewood

'plant used for colour' is the definition.
(plant used to dye things)

'a welshman would say' is the wordplay.
'a welshman' becomes 'dye' (I can't justify this - if you can you should give a lot more credence to this answer).
'say' shows a homophone (sound like).
'would' sounds like 'wood'.
'dye'+'wood'='DYEWOOD'

'as' is the link.

I've seen this clue in The Guardian.

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