How to refer to people of mixed race?
Miscegenation was coined in the US precisely to condemn such relations. Its historical context was in arguments in defense of slavery: The possibility of mixed-race marriages or sexual relations being projected as an outcome so horrible that it was good that slavery was preventing it (of course slavery led to a lot of mixed-race children too, but that was not talked about) - and anti-miscegenation laws banning marriages and sexual relations between different races that existed in the US until 1967 when the federal Supreme Court ruled the last such laws to be unconstitutional.
The reason miscegenation was taken as applying particularly to the marriage, sexual relations or offspring of white people and people of other races, is that this was seen as a problem to the white racists that coined the word. Indeed while some laws did in fact specifically ban black people from marrying people of any other race (as the race deemed lowest in the racist hierarchy such people believed in) and some blocked people of non-white races from marrying each other, the overall focus was on "protecting the white race" from the perspective of white racists.
There is no parallel word because there wasn't a powerful group of black people who spoke English as their primray language, feared inter-racial marriages and spent centuries enacting and enforcing laws to prevent it, to coin such a word.
People. Pretty sure about 99.9% of all people are mixed to some extent.
If you find someone who is really mixed - like me - then I would use mutt.
You are referring to their skin color not race, because if a person had a black dad and white mom but appeared white the question may never come up - given you don't know the mom and dad. You are referring to when people have traits (mainly skin color) of opposing ethnicity.
Multi-ethnicity if I had to label a couple that looks different.
Global or integrated or diverse if you want something cool to say or code-talk. These words would have to have context.
I believe the term you're looking for is multiracial
adj.
- Made up of, involving, or acting on behalf of various races: a multiracial society.
- Having ancestors of several or various races.
— source thefreedictionary.com
To address your second point, a person that is descended from black and non-black parent is often called a mulatto. As the Wikipedia article explains, the term has no firm definition, and it may not be not entirely free from negative connotations, but it's generally acceptable.
one word I've seen and heard used many times is inter-racial if that helps.