I have met a handful of individuals of non-black origin (Asian or indigenous) who were adopted by Black American families. In each case, the individual identifies as Black (not that they despised their communities of origin, they just didn't identify as much with them). But I've never come across any case of a non-white adoptee in a white family who identified as "white". They're always seen as "Black" or "Asian", or whatever "race" they were born into.
Why are the transracially-adopted children of black families more likely to see themselves as black, while transracially-adopted children of white families, no matter how much they are loved and how awesome their parents are, don't seem to be able to identify as white.
IMHO there isn't necessarily anything wrong with an adoptee not learning about his/her 'birth culture' and choosing instead to identify fully with the adoptive culture. I know some people feel very strongly about the responsibility of adoptive parents to ground their child with a good sense of her/his 'birth culture', but I suspect such a thing is only necessary because the larger white community that the parents belong to will never accept the child as "one of their own kind". But blacks are perhaps more open to integrating non-blacks.
I've heard from a few foreign acquaintances that adoptees in some parts of the world are seen as members of their adoptive parents' ethnic group or 'race', even if the adoptee is clearly physically different from most members of his/her community. In places like these, they have no concept of "cultural competency education for adoptive parents" like we do in the Western world. I'm not saying that's necessarily a 'bad thing' or a 'good thing'. But if it works for them, and the children are happy, that's fine with me. I'm also not implying that we in the West have to change our perspective to someone else's, but it's interesting to see that different societies have different ways of assigning identities.