If ever there were a true-life tale that laid bare the laws of South African apartheid in all their arbitrary lunacy, it’s the one dramatized in Anthony Fabian’s straight-ahead biopic of Sandra Laing, the visibly black daughter born in the 1950s to white Afrikaner parents who are as full of denial as they are of protective love. The inconvenient fact that most Afrikaners have some black ancestry spurred even greater rigidity in the application of institutional and private separatism. Played as a child by the charmingly open-faced newcomer Ella Ramangwane and as an adult by the exquisite British actress Sophie Okonedo, Sandra is turned into a human shuttlecock, classified and reclassified as black or white according to the needs of her doting but racist father (ably portrayed by Sam Neill) and the schools and government agencies who have no idea what to do with her. Every minute of Sandra’s life is defined by her color, which makes her story here feel oppressive and overdetermined at times. Yet this workmanlike, but enormously moving, movie makes the case that apartheid really does control her life, even her decision to rebel and get involved with a black man. That Sandra finally avoided becoming a walking Greek tragedy was due as much to her own survival instincts, sharpened by nonstop adversity, as to the collapse of a toxic regime.