The Purple Ghost Pepper (Bhut Jolokia) is a wide, wrinkled pepper. It starts out green, like most peppers, and when mature they turn into a darker purple.
Not all of the peppers on this plant will turn purple, some will remain red. Even the mature purple ones will likely eventually turn a shade of red when completely ripe. It has around the same SHU as most Bhut Jolokia, with some measuring over 1,000,000 SHU!