Herein lies the blurring between mainstream and porn and mainstream actors and porn actors especially. First of all it really does look like real cum. If it was fake put there by a makeup artist then it would place her squarely as remaining a mainstream actress. If however it was real then it would be reasonable to assume someone had jacked off on her face for the purposes of the movie. Even if the audience doesn't see he actual "deposit" she is still indulging in real sex for the purpose of producing a movie.