Final answer:
The extraordinary thing that happens when Pi kills the dorado is that the fish's vibrant colors fade to gray, symbolizing the loss of life.
Step-by-step explanation:
It appears there is some confusion, as the content provided does not directly relate to the original question about Pi and the three-foot dorado. However, I will answer based on Yann Martel's novel Life of Pi, assuming that's the reference point. In the novel, an extraordinary thing happens when Pi Patel kills the dorado fish that he caught. The color of the dorado fish changes spectacularly. Initially, dorado fish are known for their vibrant colors, but upon its death, the fish's colors fade to gray, signifying the loss of life. This transformation is symbolic and serves to highlight the realities of survival and mortality Pi faces while stranded at sea.