In literature a foil is a pair of characters whose differences illuminate the important characteristics in each other. Think Jekyll and Hyde, or Othello and Iago, or if you are of a younger mindset, Donald Duck to Mickey Mouse. In any event, the set up is such that you see the differences in order to enhance the main story.
Now, I realize that when a hair salon is referring to foils, they generally mean it in the literal sense. They will use actual foils to separate your hair and create colour enhancements. However, in the literary sense, the foils do indeed create a contrast that causes us to see a change in the entire style and look of your hair.
So, today’s deal is the perfect foil to drab, outdated and plain colour. The staff at RSH International can use foil to create the perfect foil.