Yikes.
1. If White is understood to be a "race," then racial groups can distinguish ethnicity, nationality, extended ancestry, phenotype, or self-identifying group. It's not clear what "white" is, legally speaking. There may be legal precedents set for other "races," for other purposes, but they shouldn't apply across the board (see 2).
2. The typical racial groups in the US are highly asymmetrical. Think of Latino, Hispanic, Black, White, Asian, Pacific Islander, Mixed, etc. In ordinary usage, these all pick out different combinations of dimensions. Compare this to another group predicate, such as color. When we identify colors, we use the identical process to distinguish pink from blue, green from orange, etc.
3. This should go without saying, but one should be able to earn a board seat no matter their race. Further, if we care at all about merit (boardrooms are peak capitalism, after all), it should be possible for a group of all Black, all White, all Chinese, or all Jewish to earn seats on a merit basis.
4. No matter how you cash out racial differences, they are ultimately superficial. Putting this much importance on superficial categories places more importance on race and (almost certainly) division.
5. The move toward "equity" is hollow. To me, it looks like rhetorical salad dressing for shifting equality to a different variable to favor one demographic over another. It's equality, but with respect to a different purpose/demographic. There is literally no way to make any law universally equal for everyone. Laws purporting equity, such as this, are passed at the expense of the majority and the *supposedly* powerful; let's stop pretending otherwise.
6. IANAL, but this is probably illegal.