Phenotypic variation in Black Head, Pastel?

I have 2 unrelated Pastel Black Heads. Both came in as juveniles expressing the same colors.

Now, one of them is not like the other. One still has a bright white belly. The other, with each shed the bright white belly scutes are being replaced with faded dark bands and the white is creeping up around the side pattern. Is this an example of phenotypic variation being expressed with age through the shedding process?

Belly photo

The one I’m talking about is in the foreground below. She used to express the same colors as the one in the background, but she keeps changing with each shed. Neat to see it happening in real time.

The original gene pool was: Pastel, black head, HGW, GHI and YB.
Thoughts, comments and witticisms always welcomed.