This may be a no-brainer, but I'm sorry I can't get it. What does the underlined mean?
Oh, I got it, it's because the old and the new ones are all white, hardly distinguishable,,,
39) Perhaps the best way that we can improve our performance is to be as creative as possible. Consider the simple task of painting a ceiling. This task is more difficult than it might seem because ceilings are nearly always painted white, and it can be hard to see exactly where you have painted. Later, when the paint dries, the parts of old paint will be annoyingly visible. Some creative person invented a type of ceiling paint that goes on pink when wet but turns white when dry. Unless the painter is so colorblind that he canít tell the difference between pink and white, this solves the problem.