This is what I have been trying, and failing, to explain on this board for years (decades if I am being honest). Whether a person is "Black" (for example) has very little to do with genetics and nothing to do with "blood" (blood is usually red among humans).
It is a cultural concept. If you want to determine whether someone is Black (or White or any other cultural concept of race), you need to ask questions along the lines of "do they consider themselves Black" and "does the society they live in consider them Black?", and other questions like that.
A person can have one Black and one non-Black parent and be considered Black. A person can have one Black and one non-Black parent and not be considered Black. A person can have one Black and one non-Black parent and be considered "mixed race". The reason you can be such inconsistencies is because race, as we are using the term here, is a cultural concept, not a scientific one. It depends on the culture, not the biology.
A funny thing about this debate about whether Harris is Black or Indian, or mixed, is that there are places in the world where being Indian makes you Black.