The British colonel is the head of the Englishmen in the POW compound Billy stops at before heading to Dresden. He is incredibly committed to hygiene and believes that once you lose interest in your appearance, you're done for. Of course Billy has never been interested in his appearance—in fact, he looks incredibly clownish and ridiculous—and yet he still manages to survive the war.
What's important about the British colonel, and the Englishmen in general, is that they still have these intense ideals about being officers and gentlemen. But they can afford to have these dreams—after all, they have spent most of the war out of commission, eating, exercising, and not having to fight. It is one of the great ironies of the book that the guys who most want to fight can't and the ones who least want to (like Billy) get sent out to witness massacres like those at Dresden.