Blue being the name of the tall blue lady is, in fact, reasonably descriptive. It makes her easy to spot from anywhere in the cookhouse and, once Strange and Joker has gone over their little etiquettes lesson, Childermass will do what he typically always does: seemingly appear out of nowhere (in this case, he was just particularly quiet, no magic involved) next to Blue Diamond.

On the bright side, there's no way in hell he'll ever be able to loom over her, so he has to settle on looking up curiously instead.

"Did they cover everything you wanted to know adequately, Ms. Blue, or would you still like to go over what spoon goes where one more time?"

He wouldn't blame her if she did. Anyone else, either, considering how pointless it must seem to some.