I went to print the Book of Patterns as a booklet but it seems there are some missing pages because Acrobat shows some blank pages in the print preview. I googled for a better PDF and found one that had one of those pages with red lines that you use a red lens to "decode". I also found one "decoded", without the red lines. I had completely forgotten about that part of the game but for the life of me can't remember what it's about. It's not in the GOG edition. Anyone remember what it's about?

Ah, nevermind. I read through the manually more thoroughly. I think it's a form of copy protection.

"Enter the Secret Weave
After choosing a Proficiency Mode,
you will be presented with a screen asking
you to enter the Secret Weave associated
with a particular Guild and Thread.
To enter the correct Weave, look at the
inside front and back covers of the Book
of Patterns included in your Loom package,
and find the Guild symbol displayed on
the screen. Then match that symbol in
the manual with the name of the Thread
(THROW, BEAT, TREADLE or REST)
also shown on the screen. When you
have found the intersection of the Guild
and the Thread, use the red gel included
in your package to read the icons of that
Weave. Use the cursor to point and click
on the corresponding screen icons in the
same order. "