Black | Red
While red/blue combination pencils are well-known, there are also pencils that have both black (graphite) and red leads. Here are a couple of old American ones, with a box:
The box describes what the pencils are for: Red lead for checking and special notations, black for shorthand and writing.
This type of pencil is more popular in Japan, judging from the many varieties –
I show both front and back because a common feature of Japanese pencils is that they have important information on opposite sides.
Note that all of these two-way pencils have black on the left and red on the right. But the one shown on the Shorthandy box is reversed!
Black/red combo mechanical pencils also exist –
The Autopoint at top is a famous example.