The meaning of each colour is:

Red:  Indicates a photo or area I dislike. I would either discard the photo or crop the red areas to enhance the focal points of each frame.

Green:  Indicates a composition that I am pleased with and would go on to edit to further improve the image.

Blue:  Shows an area where there is an area of overexposure in the frame.

Pink:  Shows an area that is out of focus where this was not my aim.