We can look at this from several ways, I like the more societal way of it, instead of "whiteness" being whatever someone wants it to be. Is someone treated in the same way as other people from a certain ethnicity? How people perceive them in everyday life (like going to the supermarket or how a cop will see them)? This is more reasonable to argue, as society is always over whatever bullshit some racist invented. With this we can argue from a sociological standpoint, like colorism, etc.

Did Richard Feynman receive treatment like a brown latino, an indian, an asian, a black person or a white person?

This is intrinsic to the question of racism and whiteness, not some vague "pale skinned" thing, and more in line with academic work, because IT'S MORE MEASURABLE, it's based on real things people endure, and on this sense, the "pale skin" makes a complete difference, from the middle of the pacific to Idk, the moon, not some random thing. If you want, I can recomend some very good books about this topic, because arguing based on definitions that aren't good starting points can't go anywhere, we need to define things not based on some common sense deffinition, but on observable and logically sound things.

Angela Davis (for an anglisized point of view) is a good starting point, because she talks about gender too, it's all related.

Edit: good starting point to understanding race and racism: https://plato.stanford.edu/entries/race/