What's there to talk about? The only time she changes her hair is in that season 3 alternate timeline episode where the Xindi win.
Clearly you lack the power of observation. There are several wigs showing her changes through the episodes. And her hairstyle is always ever so slightly adapted to the mood of the scene. Even her earpoint location changes.
We all -including Ms.Blalock- lucked out that Gloria Pasqua Casny was her hair stylist. One of the best in the biz.