Most hypo boas tend to darken as they age, especially when they get to breeding age. The trick is to figure out which babies are going to make nice adults because nice looking little boas do not necessarily turn into nice looking adults. Sometimes they do, but not always. There are many producers of outstanding hypos these days including Jeff and Jeremy. Rich Ihle, Jeff Risher, Tim Koppenhoffer, Brendan or Tim Magee to name a few.
Regarding temperament, I have found that most boas will mellow as they age. Ronne's Monstertail line can have a challenging disposition while young but calm down nicely as their teeth get bigger! LOL
Denny Rimes