For example, Google could just simply give internships to those at HBCU's, an action one may see as definitely positive. However, if for whatever reason those students fail to perform, in the eyes of the non black colleagues, stereotypes of incompetence will be created, if not exacerbated. Black people are punished more harshly for signs of incompetence of similar magnitude than Whites [2].
A somewhat similar thing happened with minority lawyers, as law schools tried to prop up the supply with affirmative action policies [1].
Things are just complicated, in general.
[1] http://blogs.wsj.com/law/2007/08/29/is-affirmative-action-at...
[2] http://www.huffingtonpost.com/2015/05/27/black-students-puni...