In most cases the purple ones fade over time.
Since I've had three kids and my youngest is 19...I know a bit about the darn things.
They do shrink and fade, mederma is the 'new' thing to try and use. Like someone else posted you need to moisturize to help prevent them to begin with. Vitamin E oil and coconut butter are what many pregnant woman use. But even with the best of care you can still get them.