Yeah but what would you call it if a black bloke marries a white woman?

Marriage is marriage. Why should the gender of either be of interest? Both Mrs Musket and I can use the term Dr and on that Dr Musket is either gender. Who needs to know otherwise? (Even more confusing for those with an interest in the gender of people, Mrs Musket is a surgeon so uses Miss in her title although we have a marriage certificate.

Marriage is marriage and if both have a dick or both have a cunt, the only dick or cunt is the one wanting to know their gender arrangements.

Calling it marriage has the advantage of describing what it is. A commitment. Civil partnership lowers it to the level of prenuptial contract to make the splitting up or death arrangements easier.