Red, Green, Purple all come in with age. How much depends on age and luck. Some are lucky and get a lot of everything, some are unlucky and get a few specs of everything. But the longer you have it, the more the colors mature.
they do not all get people. It's a crap shot. As others said the color comes with age. I have roughly 15 momma jbs that are all over 4 to 5 years old. Only 5 out of those show any kind of purple. Its something that comes with age but also genetics and sheer luck. There are far less that will end up showing purple then the ones that don't. Good job. You are lucky and have a nice jawbreaker!