If you are 90% one thing and 10% something else, than you are 2 different things. This is not one thing. You have 2 clear parts here. 12% is a great grandparent, this is very recent still. By basic definition, if you are not 100% of one thing, than you are more than one thing to add up to 100%.
Admixture is the noun and mixed is the adjective, but they are forms of the same word.
I could understand if you were talking about an event one time several hundred years ago. But when you are talking about grandparents and great grandparents who are not white, then the grandchild is also not fully white. It is ridiculous to act like this is not real. This is some strange form of wishful thinking.
If somebody is mixed race but mostly white, then he or she is mixed race but mostly white. I don't understand what is wrong with saying the truth that this is what it is. Somebody who is mostly white but partly native american is mostly white but partly native american. Native american is an asian subracial group. Both parts exist and are valid together. You can't just suppress and ignore your herritage just because you might wish it was something different.
No, at this point this is just splitting hairs.
You have endless examples of whites with some percentages of mixture, and they are still white. They incarnate as white, live in white nations, and have some mixture at a certain point in their bloodline.
The closer this is, yes one would not qualify as white, and if it isn't a small amount then yes one is most certainly mixed.
You will find this in many places if you wanted to look hard enough, as most whites are 90% to 85% in terms of racial purity. I'm not some exception here to this, neither are a solid majority of the world's population of white people.
The majority of whites you see in europe, america, eastern Europe, and many in Russia, are all white. Many whites in our world could be classified and fall within this 90% to 85% range.
As we would slide further with this, then yes one would be something else, one would be mixed.
If I looked in the mirror and I was dark skinned wirh Asian features, or black racial traits were present in myself, or any of this was the case for my wife, or my children, then I'd feel inclined to agree with you. If I was fair skinned and had other traits, then yes I'd be mixed.
I've reincarnated into a white nation, where a majority of the white people and racial collective of our race has maintained a similar racial makeup. Along with life times where I've been white, and I still am white.
What further clarification do I need to provide here? I don't see the point in this.