From the publisher:
In some worlds, Magic may not be seen as a force in and of itself. In some philosophies, magic can not be classed by types of effect, like Evocation, Illusion or Abjuration. Instead, it might be seen as a result of fundamental aspects of arcane metaphysics.
One such theory holds that all magic is a result of the principles of Colour.
You might hear of Black Magic, and think of witches, or destructive powers, or the forces of darkness. Historically, we have a tendancy to quantify black as evil. But imagine a universe where every colour has power, and each can be used by good or evil for their own aims and goals. What then would Black signify? For Black is a colour unlike any other: when you remove the light, it is what is left. Black is the absence of colour.
In such a universe, Black is the Absence of Magic, symbolizing normal matter, and normality itself, representing stability and resistance. Drawn from the Earth, Black Magic has the power of solid material to remain resilient against change and damage. It also holds the ability to oppose supernatural forces and even negate them. It is superlative protective magic, broader in scope than simple abjuration.
Occasionally there are those born with a strong connection to the Earth. This resonance can be developed into a powerful capability to evoke the Black, such that the Earth itself might answer the call of the Mage. Those with this close relationship and the powers it allows receive ultimate expression with the Chthonurge class.
Included in this product:
3 new Clerical or Mystical domains
a linked reclassification of one twelfth of the spells of the players handbook, with some new spell effects to fit the spells into Chromatic Magic Theory
a whole new character class, the Chthonurge.