blue and red pencils

There seems to be somewhat of an obsession with these double ended red and blue bicolor pencils. I can't find the specific reason they were created for, but they seem to be used for editing or correcting purposes (an editor can correct with one color and comment with another). These are also used in animation - sketching is done with red and cleanup in blue and, by holding a red gel to the drawing it would filter out the red and keep the blue. Even nowadays this process is used by photoshopping one of the colors out. Red and blue pencils are also used in construction or woodworking for its... usefulness!  They are apparently also called Postal pencils.

Because of its overuse in dictatorships and other totalitarian regimes, they are also associated with censorship. Despite that, they seem to seduce to the point that some people will even collect them. 

The most impressive collection of red and blue pencils I came upon is in Fred's Pencils blog. He has collected pencils for more than 30 years. Go on and lose yourself in his entire collection - it is quite impressive.

You may also like Bob Truby's Brand Name Pencils website. It's boasted as "the largest, most comprehensive pencil website in the world" currently having 175 Pencil manufacturers, 4,000+ different pencil images.

Edit:

If you really like pencils be sure to check out David Rees' Artisanal Pencil Sharpening. Is it a joke? Does it matter?