I work with a girl and her flatmate works in lighting. Apparently, in situations such as last night, peoples faces are lit with a subtle blue light but obviously they couldn't do that for the debate as they would not want to be accused of subconsciously attempting to influence people, so their faces were lit differently. If you looked really carefully, there were no shadows or anything on their faces and that's what made them look shiny and flat.
(That or the huuuuge amount of makeup DC seemed to be wearing...!!)