The phrase Blue Tuesdays helps to communicate the emotion of a sad color on an unimportant day. It's not quite a Monday, Wednesday, Thursday, Friday, Saturday, or Sunday. It's just a Tuesday. The feeling of a sad color on an unimportant day is the best way to show the emotions of a character dealing with the mundane-ness of life and an unexplainable emptiness that cannot be filled. We all have Blue Tuesdays.