I like your thoughts BarbaraB. When Wickham and Lizzie first speak at the Philip's it is indeed Wickham who, having already singled out Lizzie - can't fault his recognising a beautiful woman - brings up the subject of Darcy. JA says that he "asked in an hesitating manner how long Mr Darcy had been staying there." and a little later "Are you much acquainted with Mr Darcy?" Is Wickham rattled to find Darcy in the neighbourhood and is trying to ascertain how much influence/respect he has? The first question seems quite cautious and the next, perhaps, a little bolder, when Lizzie doesn't offer anything but fact. Both the ideas about red/white faces relating to embarrassment/fear could be valid in light of his mode of questioning IMO.