haha yes, carbon tends to be within the grey scale and I know I sound like the devil I just know that med students buy books specifically based on the drawings, we had a very popular book in Czech that was popular just because of the drawings even though no one could make out the words, and personally I think your drawing would pop a lot more with some coloring (or darkening in grey) of the vessels. Anatomy is such a difficult field to grasp though. How's school going anyway? Are you enjoying it? I just had a look at your blog and read embryology which made me feel slightly ill