The English idiom, “go blue,” refers to someone getting extremely cold. This idiomatic phrase is really quite literal, where extreme cold can cause part of someone’s body to become blue because of poor circulation. English speakers may use this phrase commonly to refer to somebody who is out in the cold or exposed to extremely cold conditions.
Phrases like this in English associate the color blue with lower temperatures. This is only one common type of idiomatic association for the color blue. Other phrases associate the color with either negative or positive emotions, depending on use and context, while it could also indicate surprise or other reactions.
In terms of an idiomatic association of the color blue with low temperatures, some other phrases may make the same connection. For example, the use of the phrase “blue planet” could relate to a loss of global temperature. In general, the colors red and blue may be used to indicate hot or cold temperatures respectively. The common use of these “color codes” for temperature is obvious in many consumer products and other symbolic indications in many societies.
It’s important to note that English speakers will alternately use the two phrases, “go blue,” and, “turn blue,” to indicate the same idea, that of someone becoming extremely cold. American English may favor the phrase “turn blue” as slightly more literal, where the word, “go,” is used as an idiomatic verb to mean, “become.” Many other phrases, like, “go crazy,” use the verb in the same way.
Another aspect of the use of blue to indicate cold relies on older ideas about word-color associations. In classic cosmology, blue was a color associated with not one, but two of the four classic elements of earth, air, fire, and water. More commonly, blue was associated with water, but as illustrated by the fact that “blue sky” is also a very common association, the color was sometimes associated with air as well. Some of these representations may have led to the frequent use of “blue” to indicate certain factors like temperature or other conditions.
The expression is often used in both question and statement forms. Someone could ask someone else whether, "he is going blue,” if he is concerned about his reaction to cold. Alternately, someone could say that someone else, “has gone blue,” in reaction to cold. This may only mean that circulation has been compromised, or it could indicate broader issues like frostbite. In either case, this figurative phrase links the color blue to a medical condition.