Perhaps red port city, German — yes (5)
I believe the answer is:
rioja
'perhaps red' is the definition.
'rioja' can be an answer for 'red' (I've seen this before). I am unsure of the 'perhaps' bit.
'port city german yes' is the wordplay.
'port city' becomes 'Rio' (Rio de Janeiro).
'german yes' becomes 'ja' ('yes' in German).
'rio'+'ja'='RIOJA'
Can you help me to learn more?
(Other definitions for rioja that I've seen before include "Open space (ancient Greek)" , "kind of red" , "Spanish wine type" , "wine region" , "Spanish wine variety" .)