A decorous pink and yellow (8)
I believe the answer is:
primrose
'yellow' is the definition.
(I've seen this before)
'a decorous pink' is the wordplay.
'a decorous' becomes 'prim' (I've seen this in another clue).
'pink' becomes 'rose' (colour).
'prim'+'rose'='PRIMROSE'
'and' is the link.
(Other definitions for primrose that I've seen before include "Yellow spring flower from promiser" , "Early spring flower" , "Yellowish" , "Spring woodland flower" , "grows wild" .)