The issue of writing with either blue or black pen is a matter of preference. As for me either of them is suitable to write with as long it produces the right result of using it. Pens generally, are quite incredible tools to write if only they are working as expected as one is using them.
We all know how unreliable pen could get especially how disappointing they could be in terms of its ineffectiveness when writing with them. Basically, that's why I am not really into being choosy between blue or black pen.
Most cases, I have had the chance to use either of them, but the one I've used the most is the blue pen. If I am not mistaken, most people tend to gravitate towards the use of blue pen more than the black. Apart from the colour of pen, mind you they also come in different names/brands. I have the feeling that the quality of these pens depend on the names/brands of the pens not necessarily the colour, which we should be more concerned about.