Perhaps redirect these questions to the White people that create these racial categories to protect the purity of their race. In the US, when it comes to mixed race, it's about your phenotype and lived experience. Nobody is going to look at President Obama and mistake him for a White man, despite his mixed race background(Black/White). As for the one-drop rule, it doesn't have to be enforced because racism and anti-blackness are global. Speaking about the UK, there's clearly a difference in the way Meghan Markle was perceived and treated by the British press compare to Kate Middleton.