Black Blood Question

[Daybreaker]

I love the looks of the really, really dark black blood adults - the ones who are almost solid black opposed to the black bloods who are more of a smokey grey/black.

For example (just from google search) these are two that I think are insane (in a good way!):

http://media.photobucket.com/image/b...g?t=1168364676

http://www.magix-photos.com/permamed...09D024568A917D

While I don't like the looks of the lighter/smokier ones as much like this one (as an example):

http://media.photobucket.com/image/b...tailpython.jpg

So question...is there a way to judge baby black bloods to determine which ones will grow up to become more blacker rather than grey as adults? Or is it just the luck of the draw and there's no way to determine how a baby will color up as an adult? If you can kinda guess as to which babies might be darker as adults what are some characteristics to look for? Thanks!