nope, as I said it's not really a big deal if you use blue or black, or varying different types of pens... it isn't like you get extra marks for the use of a particular pen or colour. Just use the pen you are comfortable with (and take spares!). People seem to prefer different pens because they can write neater/quicker etc with them so whichever pen is your fave...content is the thing that gets you marks.
Just don't use pink and purple pens or something silly. I was marking year 10 assignments the other day and someone wrote the whole thing in multicoloured fluoro pens things

which looked very pretty but wasn't exactly great for reading