Stop seeing red card become yellow? (4,5)
I believe the answer is:
lose heart
'yellow?' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'stop seeing red card' is the wordplay.
'stop seeing' becomes 'lose' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'red card' becomes 'heart' (hearts are red in a deck of cards).
'lose'+'heart'='LOSE HEART'
'become' is the link.
Can you help me to learn more?
(Other definitions for lose heart that I've seen before include "Here's a lot to cause courage to ebb" , "Falter in courage - or fall in love? (4, 5)" , "Mislay a card" , "get discouraged?" , "Let hopes dwindle - real ethos involved" .)