Markings on the side of a Boa's snout

Do they always fade out or do they ever stay nice and dark when the snake is older? I absolutely love the look they add to the snake and am wondering when you can tell if they'll stay or if they always fade.

For example:

http://www.1-costaricalink.com/costa...onstrictor.jpg

The one in the background I'd die to have, the one in the front just does not do it for me as much. I'm assuming the one in the back is a BCC maybe? Dunno but I know I've seen pictures of BCIs with dark markings on the side of their snouts too.

my nic boa has dark facial markings but then again he is a pretty dark boa to begin with, also has a wicked celtic cross on his head