Responses
It's also because in the OG novel the fl wrote, the ml was able to see colors after meeting and falling in love with the "OG fl". I don't know if this was mentioned already in the manhwa, but in the novel, this fact was stated many times in the beginning.
I believe he can see the color pink because he has a strong feeling towards it. He needs a driving force to push himself to fight against the curse. Maybe love can heal him, that is how typical lovestory is~