What was the significance of whole movie being black and white and one scene being colored in Schindler's list?

From the words of Cinematographer, Janusz Kaminski

“I was ecstatic to be working with Steven, and yet when we began filming it brought home the sickening reality of the Holocaust. The newsreel quality of the black and white seemed to fade the barriers of time, making [the footage] feel like an ongoing horror that I was witnessing firsthand. I think I can speak for the whole crew when I say the experience was sobering.”

It is thought by many critics that Spielberg chose to film Schindler’s List in black and white to create an extra layer of horrific realism.* And i do relate with this statement as it did played well to my mind.

For the color scenes, If I am not wrong it occur in three ways, it the starting scene, ending scene and for the girl in the red dress.

For the girl in red, there is already a question asked for it in here and from the answer of matt_black

The highlighting if the child in red (in an otherwise monochrome movie) was designed to put one thread of horror for one identifiable character in the midst of mass slaughter which would otherwise just numb the audience. In purely dramatic terms this creates a sense of identification for the audience who now have a human scale story of the elimination of an obviously innocent life. This creates a point of empathy and connection for the audience which is far more powerful and emotionally impact-ful than the statistics of mass slaughter.

For the ending scene, it was shown in present time and it seems a good decision to show it by colour. I am not sure for the starting colour scene but it must be put in contrast to ending scene.