Question

for what purpose blue coloured pens are used?​

Answer 1

In certain countries blue color or blue-black color ink was used to put signature on photocopies of the original documents to distinguish the same from original documents.

Answer 2

Answer:

Blue ink is used because it more readable and also blue color is used due to the psychological effects of it. ... These colors are also good for long reading works. for an example a normal person won't like to read the paper written with bright red ink.