I swear this thread gets made every few months. Its like a ritual or something.
It depends on your country. Whether they want to admit it or not, they're black in the united states. They'll be treated like they're black so despite their pleas of "b-b-but I'm __% white" (shout out to professor gates) that shyt won't matter. The police won't trust you any more, you won't be any more likely to get hired, none of that shyt will matter unless you can pass for white or at least something else(note how some of the first "african americans" to do something or to be featured in something were so light that they could pass for something else).We can get into the territory of "acceptable blackness" but thats a whole other can of worms.
If you're living in South Africa or Brasil or any other place with a high mixed population, you can say that you are mixed and you will have a unique culture that you can attach yourself to. There is a large enough amount of mixed people in those places so that theyre not treated like they're black by default.