I 'almost hate to say this'... but Back in the Old Days we used the white, yellow and red pencils to mark changes and corrections to "blueprints" which in those days of old were really BLUE with white lines and markings!
I still have some of each in a box that I used as a draftsman back in the late 50's!
Also in the box are my 'ruling pens', bottles of "India ink", lettering guides, compasses, and French curves!
Damn I am getting OLD!!!!!!!!!!
~~~GB~~~