Blue domination

Out of the blue...Why do we write in blue ink only?

I am referring to hand writing where blue pens and blue ink is most common colour. Sure, black is also used, and so is red, though much less frequently. Other colours are limited to only decorative usages. But why only blue? What’s special about blue ink? Internet search couldn’t help me but probably because I couldn’t search better because answer must be out there somewhere. Was blue cheaper to manufacture in early history of penmanship? Is it still cheaper or we are caught in web of historical convention? Is there any scientific proof that blue looks best on white paper, or was that mere unproven social wisdom in early history? Does it have to do with physical properties of blue ink? Are ingredients of blue most easily obtained, or blue was only ink early man could make? Was it accident of history with no reason, strengthened over time in convention, much like why we have red light for stop and green for go*?

*Even though red and green are colours most easily confused by a colour blind person, which is about one in every ten.