A civil rights legal group is challenging legacy admissions at Harvard University, saying the practice discriminates against students of color by giving an unfair boost to the mostly white children of alumni. Lawyers for Civil Rights, a nonprofit based in Boston, is filing the civil rights complaint on behalf of Black and Latino community groups in New England, alleging that Harvard’s admissions system violates the Civil Rights Act. It’s the latest effort in a growing push against legacy admissions. Backlash against the practice has been building in the wake of last week’s Supreme Court’s decision ending affirmative action in college admissions.