[jnellis]

Back in the late 70's, early 80's, Dungeons and Dragons modules (self contained adventures) used to print all their dungeon maps in light blue because photocopy machines would not pick them up. This was effectively a poor mans protection against piracy.

[Luc]

I had a manual for an assembler (Laser Genius on the C64) that used the opposite approach: the text was black but the pages were a deep red, which would theoretically photocopy to black.

In practice the original was about as much a pain to read as the photocopy.

EDIT: I remember the letters in the copy having a sort of lighter colour halo around them, which made it readable. I figured was due to the blackness of the letters pulling the limited amount of toner towards them...

[jacquesm]

DRM seems to have a long history of targeting their paying customers with abuse.

[davidpardo]

And Hewson Consultants did the same in their "interactive video adventure" Avalon circa 1984. The game -for the Sinclair Spectrum- asked for a four digit code printed in non-copy blue that came in the box. Quite a few games would do the same later, like Larry's, monkey island or Elvira, Mistress of the dark, with different approaches, but Avalon's was pure blue over white paper.