When Bell's hair is blued, she picks up that half and twists it into a pigtail to keep it out of the way while Sherlock bleaches the other side. It's not supposed to stick to anything but hair, so she's not worried about her shirt or the blue stains on her hands, but she does get out of the way so Sherlock can rinse dye off of her own hands before doing the second half.

Finally her hair is its ridiculous two-tone self, and she holds both sides out and away from her head so they don't touch each other while the dye sinks in. "Do I look suitably disastrous?" she asks dryly.