Whitish yellow growth that climbs walls (5)
I believe the answer is:
ivory
'whitish' is the definition.
(thesaurus)
'yellow growth that climbs walls' is the wordplay.
'yellow' becomes 'or' (heraldic term).
'growth that climbs' becomes 'ivy' (plant which climbs up).
'walls' indicates putting letters inside (to 'wall' can mean to contain).
'or' going within 'ivy' is 'IVORY'.
(Other definitions for ivory that I've seen before include "Shade of white" , "Off-white colour" , "Piano key" , "What may be carved" , "Creamy colour" .)