Using black ink, writing at a normal size and inside the designated areas is FAR more important than many people realise - a low resolution photocopy of one part of the page is all that examiners will see. Coloured ink and small writing may be perfectly clear on the paper but is often illegible when being marked on the computer screen. We only see PART of the question, the same part, one after another, in blurred writing. If you write anywhere on the exam booklet outside the area marked for the part of the question you are answering then you run a significant risk of losing marks. Writing on continuation paper does not have this problem - so long as you clearly label your work. So if you run out of space don't try squashing things in the margin - use the extra sheets and make sure to make it clear which question you are answering.
If your writing can't be read or is not in the correct place then you won't get the marks!