Mystia Genetics

Generally, the 7 main colors of Mystia are divided into 3 categories called properties. Element, Darkness, and Water are in the Abyssal Property; Light, Wind, and Earth are in the Holy Property; and Spirit alone is of the Force property. Each of these alone are recessive genes. But here's the weird thing. When a person inherits 2 of these genes as recessive genes, they turn into a dominate gene. If somehow, by some miracle, someone inherits all 3 properties as dominate genes, the weirdest thing of all occurs: the Rainbow property is created, as it is all 7 main colors combined.
The Rainbow property is perhaps the rarest property of all. Very few people through out the history of Terr'ahna have been born with it.
Another unusual occurrence happens with the so called Telepath gene, which has been known to pop up randomly through out the many generations of a family, but always in connection to the Force property somehow. It is thought to be a mutation of the Force property gene of some kind, because it enables the person to use what are called Psi powers, incredible abilities which uses another kind of energy that only Telepaths have, called Psi energy. Strangely enough, if a person gets the Telepath gene, that gene causes any Mystia properties the person may have to go dormant, meaning that Telepaths are incapable of ever using Mystia. Vierre is the most unusual exception to this rule.
So. Kairine Kamuya, being a Telepath, had the Telepath gene, which means she also had the Force property gene. A recessive gene on its own. Her later husband, David, had the Abyssal property gene, dominate in his bloodline. Kairine and David have a child together, Hyokune. Hyokune hence inherits the recessive Force property gene, and the dominate Abyssal property gene.
Seth Ragnara has the Force property gene, dominate, and a recessive Holy property gene. His wife, Gricia Ragnara, has a dominate Force property gene and a Holy property gene. They have a child together, Grician Ragnara, who inherits the 2 dominate Force property genes and the 2 recessive Holy property genes. For her, the Holy Property hence becomes a dominate gene, and she inherits the dominate Force property from her parents.
Later, Hyokune and Grician have a child together, Fhrana, who inherits the dominate Abyssal property gene from her father, and the dominate Force and Holy property genes from her mother, which means, against all odds, she has all 3 properties, and hence the fourth Rainbow property is formed.
Also, generally, a person is dominant in one of the colors controlled by a property. So while one person with the Abyssal property is dominant with Darkness, another might be dominant with Element. But with enough training, a person can become quite good with the other colors in their property as well. Some people who have 2 properties are sometimes, but rarely, dominant with 2 colors, one from each property.