Yellowish-white gold plant placed outside (5)
I believe the answer is:
ivory
'yellowish-white' is the definition.
I can't judge whether this defines the answer.
'gold plant placed outside' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'plant' becomes 'ivy' (ivy is a plant).
'placed outside' indicates putting letters inside.
'or' placed within 'ivy' is 'IVORY'.
Can you help me to learn more?
(Other definitions for ivory that I've seen before include "Shade of white" , "recluse's tower?" , "Substance of elephant's tusk" , "Key material" , "Jumbo's dentine" .)