Do Black Phantom Tetras Change Color With Age?

[jacblades]

the other day at work, i noticed some unusual black phantoms. they were very very black and seemed to have longer fins. i did not have a tank set up so i did not get them. when i came back today, i didnt see any dark ones but it didn't look like any had been sold.
were they just in mating mode or were these just unusual (and someone else noticed and bought them)?

thanks in advance
+jac+

 

[Lateral Line]

When courting females, the males darken, become a little more sparkly and stretch theirs fins to splitting point as they "flutter" in front of females. They do this quite regulaly, and is probably what you saw.