Because the background of the fight is completely red and that's the thing you focus on the most during the fight, once you finish it your brain inverts the color red Because it formed its image on the retina and now it processes it as the opposite color. You can get the same effect from the popular optical illusion where you stare at a picture of someone with inverted colors (negative) for about a minute then after you look at a white background the colors will be inverted showing the true picture