Mary didn't understand such sentences as "She is blue today", "You are yellow", "He has a green thumb", "He has told a white lie" and so on. And she went to the teacher Mrs. James for help.
Mary:    Mrs. James, there is a colour in each of the sentences. What do they mean?
Mrs. James: In everyday English, Mary, blue sometimes means sad, yellow afraid. A person with a green thumb grows plants well and a white lie is not a bad one.
Mary:     I'm afraid I don't understand them all. Would you give me an example for "a white
lie"?
Mrs. James: Certainly. Now I just give you some cakes. In fact you don't like it, but you don't want to let me know it. Instead you say, "No, thanks. I'm not hungry."That's a white lie.
Mary:      It sounds very interesting. Thanks very much.
Mrs. James: You are welcome. Colours are meaningful. I think you will meet more sentences like these in the future. Please come to me if you have any questions.