Why the 0.5 mm Graph Pencil has a yellow degree indicator sleeve is a bit of a mystery. Yellow is the color Pentel uses to signify the 0.9 mm lead size. Perhaps this model originated before Pentel’s color coding was codified. And at any rate, there is no 0.9 mm Graph Pencil so despite the incongruity, no color coded conflicts of consequence are created.

Let’s take this opportunity to bury a table of Pentel lead size color codes here where no one will ever find it, shall we?

0.2 mm = pink
0.3 mm = brown
0.4 mm = green
0.5 mm = black
0.7 mm = blue
0.9 mm = yellow

Pentel has models with other sizes, such as a recent model with 1.3 mm, but I do not believe those follow this convention, and if they do, they’re not drafting pencils anyway so who cares, right? Right.