For instance,
Ａの髪は黒い (1)
vs
Ａは髪が黒い (2)
(and possibly also)
Ａの髪が黒い (3)
My understanding is that they all mean the same thing, except that (1) and (3) differ by which part of the sentence is emphasized (after the particle for (1), while before for (3)). But I'm not too certain about the implication for (2) in this case.
I can't explain in grammatical terms, but I would say I disagree with you in that 1 and 3 are similar because they both emphasize the "hair" to be the focus of the statement, whereas in 2 the subject ("A") is the focus. They all have the same effect in that they all convey that the hair of A is black but to me (a native) it feels like a difference of what the person saying this wants to stress.
Not sure if you get what I'm saying ... I can elaborate further if you wish.
