Supporter to wear yellow (5)
I believe the answer is:
donor
'supporter' is the definition.
(I've seen this before)
'wear yellow' is the wordplay.
'wear' becomes 'don' (to don an item of clothing is to wear it).
'yellow' becomes 'or' (heraldic term).
'don'+'or'='DONOR'
'to' is the link.
(Other definitions for donor that I've seen before include "A giver, perhaps of blood" , "Almsgiver, benefactor" , "Charitable giver" , "patron" , "Philanthropist" .)