Snakes can potentially change color with every shed. Robin (rabernet) frequently posts how her lemon pastels seem to go through an ugly duckling phase, then brighten up.

This is a rare example, but check out this thread to see just how much color change can occur in a single shed:
http://www.ball-pythons.net/forums/s...ad.php?t=62581

Also, you can definitely do a lot with selective breeding, so you have a good chance of improving on the looks of your snakes by pairing them to the right mates.

My pastels had the same father, but different mothers. My female pastel is really gorgeous, one of those ones that some people would mistake for a super, and although I was lucky enough to get the pick of the clutch, her sisters were almost as nice. Unfortunately, there were no males in that clutch, so I got her half brother. The pastels in that clutch were still better than average, but the best one was noticeably lower in quality than the worst from the first clutch. Bottom line is that even in a single generation, careful selective breeding can make a difference, and similarly, if you aren't selective, even a single generation can make a difference in the opposite direction. Of course there are no guarantees, but that is what makes it so exciting!