Confucius said: “A loyal minister remonstrates with his ruler in five ways. The first is by guile. The second is blunt and plain. The third is with a humble manner. The fourth is direct. The fifth is by allusion. One measures the ruler and acts accordingly. I would follow remonstrance by allusion.” The passage is in the Family Sayings of Confucius (孔子家语).
An old commentary in the same text explains the fifth way, fengjian (风谏). It stays noncommittal and keeps the speaker clear of blame and harm.