Brown is a 'muddy' color, one created by blending several different colors. It is inherently not 'pure' like a primary color is. Conflicting emotions, frustration, anxiety, annoyance, and anticipation are all represented in browns. Obviously, Micole is demonstrating annoyance here, an attitude of mixed emotions (surprise, anger, confusion). If she were to become more angry than surprised or confused, the brown would lean towards terracotta, more confused would result in a sepia or greenish-brown, more surprised would present itself in ochre or yellow-brown.
Oh, a random note here: Khromatai can change all their fur, including the crestfur or 'hair' on their heads. Chemistry in the makeup of the different fur fibers (they have 5 types) allows controlled changes to certain areas. Micole is demonstrating her colorshift talent as a skill by the fact her hair does *not* change colors with her body. A true infant or emotionally uncontrolled khromat would have all their body the same color, natural temperature variations among the fibers and locations would gradiate that color -- in this current example, if Micole were untrained or not in control, her frustration color would be all over brown, her hair being a shade or two darker than her body.
When you next see either of these new images (or more as I upload them), they'll be used as their expressions dictate and not just for 'here's my purdy picture' demonstrations. :D