Why does the middle one have dark roots, is that because of some shit that happens later in the series?

bunkhead said:

Why does the middle one have dark roots, is that because of some shit that happens later in the series?

The novel covers up to 12 don't seem to suggest it anyway. Design-wise I'm guessing the 3 Tanyas are manga Tanya, novel Tanya, and anime Tanya.

A small shift in artstyle in the later volumes of the light novel added the darker hair.
Shoutout to dfens for providing this information.