I never got why she was the only one in color
One Spielberg quote that was taken from an interview was this "America and Russia and England all knew about the Holocaust when it was happening, and yet we did nothing about it. We didn't assign any of our forces to stopping the march toward death, the inexorable march toward death. It was a large bloodstain, primary red color on everyone's radar, but no one did anything about it. And that's why I wanted to bring the color red in."
However to go a bit deeper, then take a paragraph from this site http://funadvice.com/r/bt6ldlfpca4
The little girl's jacket is red so that she stands out from the masses. When color is used, it makes a point and an impression. And Schindler´s soul is touched by the child, he feels her pain, cries for her. The plight of the one little girl in red touches him in a way the shear numbers make unreal, it is easy to get lost in numbers. He transforms the faceless mass around him into one real palpable human being. This one child is a symbol of all the 6.000.000 victims, exposed to ruthless slaughter. The little girl in the red coat footage gives a feeling of hope. You think that she may be able to get away, that she has a chance. But then you see her later, and she is dead. She has already been killed, and you feel the despair and a lot of anger towards these Nazis. How could they kill something so innocent?
Stalin famously noted, "One death is a tragedy; a million is a statistic." I don't doubt any of your answer but I do take exception to Spielberg's idea that America, Russia, and England knew about the Holocaust as it was happening. We knew that the NAZI regime was persecuting Jews but war documents show that the US had no idea the extent of what was happening until Allies invaded Germany. When Russian soldiers discovered and reported the NAZI death camps the US dismissed these reports as propaganda. We didn't believe it until US soldiers confirmed what the Russian soldiers reported.
My teacher made a point that she is supposed to represent the innocent. As she is just a child, she is innocent.
Thank you both it cleared things up for me thank you