The color of the book provides information on which class they are:
orange for Body Warrior, red for Mental Warrior, blue for Weapon Sura, green for Black Magic Sura, purple for Archery Ninja, pink for Blade Ninja, brown for Dragon Force Shaman, gray for Healing Shaman, light green for Lycan
There are two books to the Masters unsubstantiated rumors:
They should have a higher probability than normal skill books. We do know that they can also fail with Concentrated Reading (2.5-fold chance). The probability must be below 40% and therefore can at best marginally different from skill books, which is 30%.
There are some reports that in rare cases Technology levels skipping.