In the novel the circumstances Pi comes across are incomprehensibly dire and impossible to relate to. Pi, as a mathematical term, is a irrational number with a nearly never ending amount of decimals. It is so long that the human mind cannot understand it and it is simply written as 3.14. Pi's name represents the very story and the circumstances he faces.
Richard Parker is a symbol of Pi's will to survive. Pi, who is normally peaceful and religious, cannot face that he murdered a man and ate a man. Therefore he separates his will to survive form himself in his fantastical narrative in order to stop himself from facing reality.
Orange represents hope, as Richard Parker (Pi's will to survive), the whistle he tames him with and the life buoy on which he fishes are all orange and these are the things that allowed Pi to survive.
As Pi has lost everything during the sinking of the Tsimtsum he must start anew. This is represented by the ocean which symbolizes a baptism, cleansing or a rebirth/fresh start.
Pi's story follows the structure of a hero's journey. He is set out a journey, faces many ordeal, overcomes all obstacles and finds his reward (he finds god), and he sets back into society.