"Bite" can mean a forceful personality (see my Eileen for that!) but it can be a quiet character simply determined not to be pushed around any more. The "bite" comes from what drives them. And motivation is crucial to get right. It's got to be important enough to your character for them to risk their life if necessary.
So what makes your characters memorable? Yes, a striking physical appearance can help here but for me it is the dominant trait that matters most. (Even if that dominant trait is suppressed, perhaps because it's not publicly acceptable, the story will revolve around the struggle to keep that suppressed and what happens if all goes wrong - as I think it inevitably would).