This has been talked about for many years. Here is a bit Roger Ebert wrote http://www.godamongdirectors.com/tarantino/faq/secrets.html
"There were two visual touches we discussed a lot. One is the golden glow which mysteriously suffuses the screen as Jules and Vincent open fire in the apartment; is it connected somehow with the briefcase? Does it link the devil's case with the devil's work? Another is a curious head-on shot of Bruce Willis, who looks straight at the camera while Marcellus Wallace instructs him to fix a fight. The lighting is used to shadow exactly half of Willis' face; a line runs down his forehead, nose and chin. Or ... is it lighting? The line of demarcation between light and shadow is so sharply defined that we wondered if makeup was used to augment the effect. We looked at the scene repeatedly using freeze frames, but were unable to decide."
SECRETS OF 'PULP FICTION'(5/95)