TSR trialed an obscure extension to their Endless Quest gamebook line, “Crimson Crystal”. CC’s gimmick was the use of a square of red-tinted film to reveal information on specially-designed pages in the book (see photos below).
TSR had been experimenting with the same idea in its published adventures around 1985. Many game lines saw products using Magic Viewers: Indiana Jones, Marvel Super Heroes, AD&D’s Midnight on Dagger Alley (MV1), D&D’s Mystery of the Snow Pearls (CM5), and no doubt others I’m forgetting.
Renegades of Luntar (Endless Quest Books: Crimson Crystal Adventure 3)
1985 … Roger E. Moore & Keith Parkinson (cover) & Mario D. Macari (interior art) … TSR 8929 … ISBN 088038218X
You are Joshua MacKenzie, a young astronaut living at Ares Base on Mars in the year 2085. While exploring, you find the remains of a renegade society that lived thousands of years ago. Among those remains are Searcher, a fantastic ruby computer/laser weapon, and another defense computer that is preparing to destroy the new “invaders,” the Earth people at Ares Base, and perhaps the Earth itself.
The destruction is about to start, and only you can stop it. You use Searcher’s help to translate Luntarian writing and fight strange and powerful robots.