The numbers are used to represent sex.
Boy.Girl.Unknown
So 1.2.3 Pastel Ball Pythons would be 1 Male Pastel, 2 Female Pastel, 3 Pastels of unknown gender. The third number is less common, sense it is less common for people not to know the gender of their animal.
Check this out:
http://www.ball-pythons.net/forums/s...ad.php?t=69059