I do know a lot of inter-racial couples and it does brings a unique challenge where each person brings their own unique beliefs, biases and cultures with them. Sometimes theses things can co-exist alongside each other while at other times they can bring conflict. The people just have to be aware of what each one is bringing to the relationship and to try and work out these items.
Every person brings their own unique beliefs, biases, and culture. If you a positing the theory that inter-cultural marriages can be difficult, I agree. Inter-racial couples brought up in the same culture may not experience more difficulties if they choose to focus on what brought them together and not the difference in the amount of melanin in their skin. My white mother and black dad were married for 54 years before Mom dies almost 3 years ago. My white wife and (mixed race) I have been married for 25 years and counting.