So the million-dollar question: why are pencils yellow? It's ingrained in our heads that pencils are supposed to be bright yellow, even though it's not heralded as a professional nor particularly studious color. They look pretty cheap too. Hard to believe that the ubiquitious yellow color was chosen by a high-end manufacturer looking for an exotic color to set their pencil apart from the generic brands.
It wasn't even the Dixon Ticonderoga you know and love but Koh-I-Noor- a European brand named after a diamond and now known more for calligraphy and drafting supplies. At the time, yellow was considered an exotic color that hinted at Chinese origins. Because nothing says quality like something made in China. It was such a big hit that everybody jumped on board and did the same thing, to the point where yellow became an industry standard and lost pretty much all its meaning. It's no surprise that Koh-I-Noor got out of that gig.
So for those slaving away at finals, now you know why the pencils you use for tests are yellow. Although, as an added punchline, it's worth pointing out that test scanners now read and accept some mechanical pencils. In fact, almost all Bic mechanical pencils are Scantron-certified.