Above is a juvenile snake.  Below is a black phase.  Babies change as they grow.  After their first shed you can tell what phase they are going to be.  There is no correlation between overall color phase and sex, but females retain the post-ocular stripe (between the eye and the jaw) while in males it becomes obscured with pigments.  This is most easily seen in yellow variety snakes because in black phase snakes the dark pigment covers the head and completely obscures the pattern.
    While virtually all individuals in a population use the densite throughout the winter, gravid females are most common in the summer.  The males and non-gravid females migrate up and down the mountain seeking food and mates, while the gravid females bask in the sunlight near the den.  Birthing occurs in late summer.  Individual females don't birth every year.  One year starting around three or four years old the female will mate and the following year she gives birth.  She may mate the next year and space the births two years apart, but it seems most snakes in the northeast birth triennially.