Shrimp, before its prepare, is a extremely unappetizing gray-blue shade. This shade, it is about to change, is the exoskeleton( you know, the shrimps external skeleton ).
Now, to explain how that exoskeleton switches pink we have to get scientific on you. Here we go: the exoskeleton contains carotenoids( who the hell is tints) called astaxanthin. It is these carotenoids that are what give salmon its pink shade. Before the prawn is cooked the astaxanthin is covered by protein chains called crustacyanin. The protein chains in fact wrap up the astaxanthin, disguising its lovely pinkish-red color.
But heat loosens the help these protein chains have on the carotenoids and releases the astaxanthin, moving the prawn its nice tint of pink. This is the same reason lobsters turn red when you cook them.
One more enjoyable fact: if youve ever heard that flamingos are pink because they eat prawn, its because of this same carotenoid. While flamingos eat prawn that still show blueish gray( they dont have the luxury of cooking them before feeing ), the crustacyanin protein series dissolves in digestion secreting the carotenoid that constitutes flamingo feathers more pink.