When English speakers mention the idiom "to feel blue," they are expressing sadness or a similar emotion. This phrase is used in many ways in the English language, including in a musical genre, “the blues,” which not only involves a specific musical structure, but also a lyrical element that focuses on hardship and suffering. Feeling blue is an idiomatic phrase that highlights a cultural association between a certain color and an emotion.
It’s important to note that while the use of “feel blue” does not have a precise opposite corollary idiom, there is the idiomatic use of either “sunny” or “bright” to represent positive emotions. Also, blue is not the only color in the palette that is associated with emotion. Other “emotional colors” work in similar ways, where an intangible feeling is linked to a visual color.
Different idiomatic phrases in English refer to red to indicate anger. Someone might say “I saw red” indicating that the speaker was extremely angry. Similar ideas exist in phrases like “red rage” or “nature red in tooth and claw,” where the latter represents that ferocity of the natural animal world.
Many other phrases use the word black to indicate pessimism, cynicism, anger or depression. If someone has a “black day,” he or she is having an especially bad day. The same kind of idea is also used in other phrases like “black mood.”
Different theories abound on the exact origin of the term “feel blue” or “feeling blue.” Some point out that the water in human tears may have been perceived as “blue” in physical depiction such as cartoons. Blue is also a “cool color,” which is associated with more subdued emotional states. It should also be noted that a bluish tent to the skin is often an indication of poor health. Perhaps not surprisingly, darker shades of blue are more commonly associated with sadness than lighter shades.
Although there are a wide variety of phrases linking blue with sadness or a negative emotion, there are also others that associate the color blue with more positive emotions. Many of these rely on the idea of a light blue sky with white balance. The use of the phrase “blue sky” can be associated with happiness, openness, as well as the more tangible idea of good weather. This can be confusing to those who are not familiar with all of the idiomatic uses of color phrases. Largely, beginning English speakers can remember that the most common and simplest phrases, including “to feel blue,” usually associate blue with sadness.