Red tome: In logical argument and mathematical proof, the therefore sign, ∴, is generally used before a logical consequence, such as the conclusion of a syllogism. The symbol consists of three dots placed in an upright triangle and is read therefore. While it is not generally used in formal writing, it is used in mathematics and shorthand.
LOGIC
3 dots could be also the symbolism of a place of interest and with the color red it can mean
DANGER AND ADVENTURE
Purple tome: A crown is the traditional symbolic form of headgear worn by a monarch or by a deity, for whom the crown traditionally represents power, legitimacy, victory, triumph, honour, and glory, as well as immortality, righteousness, and resurrection.
The color purple is often associated with royalty, nobility, luxury, power, and ambition.
POWER AND ROYALTY
Grey tome: the British association of magicians, traditionally forbidden to reveal any of the secrets of their art. 2. ( not capitals) a group of influential people involved in a conspiracy.
SECRETS OF DARK MAGIC
Green tome:The hammer is essentially a masculine force, and when striking or crushing it represents justice and revenge. The hammer is not only a tool; it represents might. When paired with an anvil, represents ANDROGYNE, and with that often fertility and creation. The hammer is the thought while the anvil is the brain.
JUSTICE / FERTILITY
Blue tome: Blue is a primary color across all models of colour space. It is the color of the ocean and the sky; it often symbolizes serenity, stability, inspiration, or wisdom. It can be a calming color, and symbolize reliability.
And with that symbol that is perfectly simetrical I deduct that is a symbol that means the balance in the perfect knowledge.
WISDOM
This are my thoughts , after a research thats what I think that the tomes means by its symbols and color.