Why is blue ink most commonly used for writing?
As with many historical questions, there are probably many factors involved. This website gives some history on ink and suggests that blue ink was the first color developed after black. That probably goes a long way toward explaining its popularity. Also, the utility of ink is in its legibility (in most applications) and legibility comes from contrast. After black, blue would provide the most visual contrast on white (and light) papers and thus be the easiest of the non-black colors to read. Beyond that, blue has also traditionally been one of the most popular “favorite” colors. It is likely that all these factors, and more, combined to make blue ink popular for writing.
