蓝颜红颜
[lán yán hóng yán]
This phrase generally refers to close friends who are not romantically involved but have a very deep relationship. Specifically, '蓝颜'(Lányán) means male friend, and '红颜' (Hóngyán) means female friend for a man. These types of friendship are often filled with trust and companionship that go beyond typical platonic friendships.